New Terrorism, New Law? Analysing the Legality of Using Force Against non-State Actors - 2007

University for Peace – Department of International Law and Human Rights

University for Peace Universidad para la Paz

Department of International Law and Human Rights

Thesis

Gabriel E. ChavezTafur Bello

New Terrorism, New Law?

Analysing the Legality of Using Force Against non-State Actors

23rd June 2007


Department of International Law and Human Rights

Thesis

Gabriel E. ChavezTafur Bello

New Terrorism, New Law?

Analysing the Legality of Using Force Against non-State Actors

23rd June 2007

This thesis is submitted in partial fulfillment of the requirements for the degree of Master of

Arts in International Law and Settlement of Disputes.

University for Peace Universidad para la Paz

The only established exception to the general prohibition to use force unilaterally is self-defence. Three conditions must be fulfilled: the occurrence of an armed attack, attribution of responsibility for the commission of such attack, and that force be executed under the parameters set forth by what is necessary and proportionate. Though generally accepted in inter-State relations, application of these norms to acts perpetrated by non-State actors with violent methods and transnational reach is deeply contested. Opinions vary: while some vouch for the need to rewrite the laws, others believe they should be reinforced, discarding any re-interpretation whatsoever. The following paper will examine these positions in four parts: first, by describing the use of force paradigm as it currently stands under the UN Charter and customary international law. Secondly, through the analysis of the concept of “armed attack” and its applicability when dealing with non-State actors. Thirdly, by reviewing the laws of attribution of responsibility to a State for the actions of private groups, assuming that between the ‘victim’ State and a non-State aggressor will always stand the political independence of another State. Finally, it will discuss the notions of responding vis-à-vis anticipating an attack, and their conformity to the requirement of resorting to force only when absolutely necessary and proportionate.

Gabriel ChavezTafur International Law and Settlement of Disputes

University for Peace – Department of International Law and Human Rights 3

Table of Contents

Table of Contents 3

Introduction 4 New terrorism: new conflict? 4 Responding to the threat 6

Part One. Unilateral use of force in inter-State relations 9 Article 2(4) and the general prohibition 10 The exceptions to Article 2(4): self-defence 11 The concept of armed attack 13 Necessity and proportionality 17 Summary 18

Part Two. Resorting to self-defence against non-State actors. 20 Non-State actors and international law 20 The ‘armed attack’ requirement 23 State practice and opinio juris 30 Summary 34

Part Three. Responding to an armed attack: non-State actors and State responsibility 35 State responsibility for non-State actions 36 State sponsorship 38 Contemporary thresholds for State responsibility 41 State support 43 Summary 48

Part Four. Responding or preventing? Necessity and proportionality in the use of force against non-State actors 50

Necessity against non-State actors 50 The necessity to deal with future attacks: Anticipatory self-defence 53 Choice of targets and the principle of proportionality 54 Summary 55

Conclusions 56

Bibliography 57

New Terrorism, New Law? Legality of Using Force Against non-State Actors


Introduction

On Boxing Day, 1968, two members of the Popular Front for the Liberation of Palestine

managed their way into the runway of Athens Airport, pointed submachine guns toward the

windows of an El Al Boeing 707 ready for take off, and pierced the aeroplane from tail to

cockpit. One of the passengers died; 50 others survived the attack. Two days later, Israeli

commandos descended from six helicopters into the runway of Beirut’s International

Airport and attached explosives to thirteen planes belonging to Arab airlines. Though there

was no loss of life, the destruction of the aircraft was estimated at over 40 million US

dollars.1 After two days of deliberation, the Security Council unanimously stated its

condemnation of Israel (15-0), “for its premeditated military action in violation of its

obligations under the Charter” and issued a “solemn warning that if such acts were to be

repeated, the Council would have to consider further steps to give effect to its decisions”.2

More than 30 years and 1,100 Security Council Resolutions later, the United States launched

Operation Enduring Freedom and invaded Afghanistan, with the intention of overthrowing the

Taliban government and confront Al Qaeda, a shady organization allegedly responsible for

the attacks on New York on September 11th, 2001. Far from a condemnation, however, the

US received the “whole-hearted support” of the European Union3 and NATO’s “indication

of willingness” to act in collective self-defence. But most importantly, the operation was

conducted with the Security Council’s “readiness to take all necessary steps to respond to the

terrorists attacks of 11 September 2001, and to combat all forms of terrorism, in accordance

with its responsibilities under the Charter of the United Nations”.4

New terrori sm: new con f l ic t? Both cases so briefly described above share many commonalities: in both a State responded

to an attack on its civilians and property, perpetrated not by another State but by an

1 Falk, Richard A. The Beirut Raid and the International Law of Retaliation. The American Journal of International Law. Volume 63. 16. 1969. 2 Security Council Resolution 262. 1968. http://daccessdds.un.org/doc/RESOLUTION/GEN/NR0/248/43/IMG/NR024843.pdf 3 Press Release, Brussels, 7th October 2001. 4 Security Council Resolution 1368. 2001. http://daccessdds.un.org/doc/UNDOC/GEN/N01/533/82/PDF/N0153382.pdf



organization comprised of individuals with transnational operational means and violent

methods. Both the US and Israel planned and executed military responses, invading the

territory of another State. Above all, both countries employed the same legal justification for

their actions: self-defence after being attacked by a non-state actor.

The international community’s response to the argument, however, has varied greatly over

the years. While in 1968 Israel’s case proved to be completely unconvincing even to its allies,

in 2001 the same legal justification found no opposition either from the Council or the

General Assembly, where a unanimous resolution condemning 9/11 was also passed.5

For sure, 9/11’s impact in world affairs is undeniable. Practically every legal scholar

acknowledges the attacks and the international response that followed as a turning point,

whether it’s President Bush declaring a ‘different kind of war against a different kind of

enemy’,6 or Professor Guruli admitting that “the attacks of September 11th illustrate that the

current doctrine on self-defence, as embodied in the UN Charter, is not comprehensive

enough to deal with challenges posed by this global era of terrorism”.7

Yet for all the change experienced by the international community, there is still doubt as to

what extent recent events have actually changed or will in effect cause the rewriting of the

laws of self-defence. Although Müllerson acknowledged this as a possibility when he wrote:

“For States’ representatives to sit down and draft new rules of jus ad bellum is not sufficient

that the political structure of the world changes radically, but such a change has to be

accompanied by a ‘bang’ that would be ‘big’ enough to shock the world to such an extent

that most nations would believe… that things cannot go on any more like that, that enough

is enough”8; in his view, 9/11 did not cause such a big bang.9

5 General Assembly Resolution 56/1. 6 Bush, George Jr. Source: http://www.whitehouse.gov/news/releases/2005/08/20050822-1.html 7 Guruli. Erin L. The Terrorism Era: Should the International Community Redefine its legal Standards on Use of Force in Self-Defence? Willamette Journal of International Law and Dispute Resolution. Volume 12. Page 102. 8 Müllerson, Rein. Jus ad bellum: Plus ça change (le monde), plus c’est la meme chose (le droit)? Oxford University Press. 2002. Page 152. 9 Ibid. Page. 153.



The fact of the matter is, that while some authors demand and justify acting outside the

provisions of the UN Charter and current international law, others still vigorously defend the

relevance and applicability of the UN Charter, rejecting any challenge to “the principles

which, however imperfectly, world peace and stability have rested for the last 58 years”.10 In

short, as Christine Gray describes, it is still quite “open to question whether September 11th

have brought about a radical and lasting transformation of the law of self-defence, or

whether its significance should be narrowly construed [as] a one-off response to a particular

incident based on Security Council affirmation and (almost) universal acceptance by

States”.11

Responding to the threat There is no universal definition for terrorism under international law. Although several

attempts have been made in the past decades, only some basic elements are generally

accepted as central to a terrorist act: the use or threat of violence, psychological impact

and/or fear, the pursuit of a political goal and the deliberate targeting of non-combatants or

civilians.12 As to the perpetrators, this paper will focus only on terrorist acts carried out by

organizations with cross-border operational capabilities. Due to their international character,

these organizations will be referred to as non-State actors.

International law allows for two types of response against terrorist acts: peaceful and

coercive.13 Peaceful responses include the various international treaties that deal with

terrorist acts, as are the hijacking and sabotaging of aircrafts (1970 Hague Convention and

1971 Montreal Convention), attacks on internationally protected persons (1974 New York

Convention), and the taking of hostages (1979 New York Convention).14 This approach is,

of course, very limited, as treaties are only binding on those States who provide their consent

“and, in particular, not enough States that actually count in this field are parties – that is, those

10 Annan, Kofi. Speech given at the opening of the General Assembly Annual Session, held on 23rd October 2003. Source: http://www.un.org/webcast/ga/58/statements/sg2eng030923.htm 11 Gray, Christine. International Law and the Use of force. Oxford University Press. 2004. Page 160. 12 Record, Jeffrey. Bounding the Global War on Terrorism. Strategic Studies Institute of the US Army War College. http://www.strategicstudiesinstitute.army.mil/pdffiles/PUB207.pdf 13 See generally Cassese, Antonio. The International Community’s “Legal” Response to Terrorism. International and Comparative Law Quarterly. Volume 38. July 1989. 14 Cassese also lists provisions in the Geneva Conventions and other Humanitarian Law, as terrorism, in his view, can be as easily committed during times of armed conflict as during peace. He also briefly mentions bilateral and extradition agreements.



States on whose territory terrorists seem consistently to end up”.15 Similarly, none of the

treaties contain effective enforcement provisions, there is little light on what terrorist acts

can be considered “political offences” and are therefore exempted from extradition, and,

fourthly, it is too easy to avoid the application of the “prosecute or extradite” rule present in

such treaties by simply not capturing suspected terrorists.

This has led to some States to prefer to resort to coercive responses, found in the provisions

and customary international law that deal with the use of force by States. It is this scope of

responses that the following paper will attempt to tackle, in four sections:

The first part will describe the use of force paradigm, as it is conventionally portrayed under

customary international law and the UN Charter. Here the analysis will focus on the

development of the general prohibition on the use of force, its international status as jus

cogens, and its attempt to safeguard international peace and security. Following, the paper will

deal with the only unilateral exception to this prohibition, found in Article 51 of the UN

Charter, as well as the interrelation between customary international law and the Charter.

Thirdly, attention will be directed to the concepts of necessity and proportionality, as the

parameters under which self-defence can be applied.

The second part will dig deeper into the concept of use of force in self-defence, focusing on

its use against international non-state actors. First, it will discuss the validity of applying

international law to the actions of international persons other than States, and the similar

question of whether States should be restricted by international law when responding to

actors that do not abide and are not bound by it. Secondly, the concept of “armed attack”, as

a prerequisite for self-defence, will be applied to terrorist actions, from three angles: that of

the perpetrator (ratione personae), that of the scope and scale of the attack itself (ratione

materiae), and by studying the evolution of State responses to similar attacks.

Thirdly, this paper will deal with the question of responsibility for the attack. As is well

established, international law has conventionally been structured to deal with and respond to

States. In that sense, it is not clear who, in the international arena, is to blame for the actions 15 Cassese. Supra note 13. Page 593.



of non-state actors. Can a State use force against anything other than States? To deal with

this question, the general theory of State responsibility will be described, as the different

thresholds developed over the years to determine accountability of States toward the actions

of private individuals operating within their borders.

Finally, this analysis will focus on the limitations of a State willing to act in self-defence

against non-State actors. Particularly, this part will apply the concepts of necessity and

proportionality to the sui generis nature of terrorist attacks, and will discuss the notions of

retaliation and anticipatory self-defence – two concepts that have become, with regards to

their implementation in the field, particularly hard to differentiate.



Part One. Unilateral use of force in inter-State relations

The general prohibition to use force against another State, as it exists today in international

law and is codified in the UN Charter, is a fairly recent development. For centuries, it was

the doctrines of bellum justum and later the ‘right to war’ which, rather loosely, held the

parameters under which a nation could decide to wage war against another.1 Only after the

First World War the notion of a general prohibition to resort to war was imagined.

The principle was codified for the first time in 1928, with the signature of the General Treaty

for Renunciation of War as an Instrument of National Policy, also known as the Kellogg-

Briand Pact. Under this treaty international law progressed from jus ad bellum to jus contra

bellum, allowing States to go to war only in the following circumstances: Self-defence, as it

was specifically noted by the principal signatories prior to the conclusion of the Pact; as an

instrument of international policy (vis-à-vis national policy, or national interests), meaning

war could be waged to uphold international law or against a violation of international

obligations; and finally between contracting and non-contracting parties.2

With this in mind, this Section will attempt to describe in detail the current unilateral use of

force paradigm as it is understood today. To do so, it will focus on the general prohibition as

presented in the UN Charter, and its implications. It will then describe the two exceptions

contemplated in the Charter, namely self-defence and collective measures taken by the

Security Council, and will present the debate regarding the differences (and relevance)

between pre-Charter customary international law vis-à-vis treaty law. Thirdly, this part will

narrow down its focus to deal with self-defence, as the current universal argument used by

States to justify unilateral use of force, in the terms it is currently accepted under

international law: the concept of “armed attack”, complemented by the notions of necessity

and proportionality.

1 For more information, see generally: Dinstein, Yoram. War, Aggression and Self-defence. Cambridge University Press. Fourth Edition. 2005. 2 Dinstein. Supra note 1. Page 67.



Arti c le 2(4) and the general prohibi t i on As it stands today, the general rule of international law regarding the use of force by one

State against another is that it is prohibited. This is explicitly stated in Article 2(4) of the UN

Charter, which reads: “All members shall refrain in their international relations from the

threat or use of force against the territorial integrity or political independence of any State, or

in any other manner inconsistent with the Purposes of the United Nations”.3

Although very clear with regards to whom is the article aimed at, i.e. members of the United

Nations and therefore all States,4 ever since it’s drafting there has been considerable

controversy around what is force prohibited against. There are two approaches to this:

On one hand, the literal interpretation, which argues that the use of force against another

State is prohibited if and only if such force is aimed at ‘the territorial integrity or political

independence’ of the attacked State, or following the same logic, provided that it is in no way

‘consistent with the purposes of the United Nations’. Although this leaves open the door to

using force for a wide variety of purposes not inconsistent with the United Nations, the

argument has been used almost solely by scholars rather than States. Two exceptions to this

were the Corfu Channel Case, brought by Albania to the International Court of Justice against

the United Kingdom5; and the Entebbe Rescue, after which Israel argued its use of force

against a hijacked aeroplane did not affect Uganda’s integrity or independence. Both times

the arguments were rejected, first by the ICJ (regarding the UK-Albania case6) and then by

the Security Council (concerning Israel’s use of force7). Though more recently some scholars

have insisted in this line of argument to justify use of force for humanitarian purposes

(NATO’s intervention in Kosovo, for example), States, however, have generally shied away

from it.

3 UN Charter. Source: http://www.un.org/aboutun/charter/ 4 The only territories not to form part of the UN are Antarctica, Vatican State, Western Sahara and the Palestinian Territories, which currently hold UN Observer status. 5 After having employed military force to recover evidence in Albanian waters that may indicate Albanian responsibility in the destruction of two British warships, the UK argued that its use of force had in no way affected Albanian territorial integrity or political independence. 6 For detailed information on the Corfu Channel case and ICJ rulings, see: http://www.icj-cij.org/docket/index.php?p1=3&p2=3&code=cc&case=1&k=cd 7 Security Council 1942nd Meeting, paragraph 102.



On the other, a wider, all-encompassing prohibition to the use of force is generally

considered to be the original intention of the drafters of the Charter, and should therefore

be the appropriate way to read Article 2(4). As Dinstein explains, “the travaux préparatoires of

the Charter indicate that the expressions ‘territorial integrity’ and ‘political independence’ had

not originally been included in the text and were added for ‘particular emphasis’, there being

no intention to restrict the all-embracing prohibition of force”.8 This reading has also been

subsequently confirmed by various international bodies, such as the ICJ (e.g. the Nicaragua

case) and the General Assembly (e.g. the Friendly Relations Declaration and the Definition of

Aggression, which specifically states that ‘no consideration of whatever nature, whether

political, economic, military or otherwise, may serve as a justification for aggression’9). In

short, as it stands today, Article 2(4) prohibits all uses of force between States, and is

considered to be the codification of customary international law.10

The except ions to Art ic l e 2(4) : s e l f -de fence The UN Charter provides four exceptions to the general prohibition of Article 2(4): self-

defence, use of force authorized by the Security Council, use of force by the five permanent

members before the Security Council is functional and use of force against the “enemy”

states of the Second World War. Little will be said with regards to the last two exceptions, as

none of them have fulfilled any role in international relations since 1945.

Concerning the use of force authorized by the Security Council, found in Chapter VII of the

UN Charter, the exception to 2(4) lies in the Security Council’s power to determine what

constitutes “any threat to the peace, breach of the peace, or act of aggression” and

consequently “decide what measures shall be taken”,11 including “such action by air, sea, or

land forces as may be necessary to maintain or restore international peace and security”.12

8 Dinstein. Supra note 1. Page 68. 9 General Assembly Resolution 3314. Source: http://daccessdds.un.org/doc/RESOLUTION/GEN/NR0/739/16/IMG/NR073916.pdf? 10 In fact, the International Law Commission, in its commentary on the draft of the Vienna Convention on the Law of Treaties, went as far as to consider Article 2(4) a ‘conspicuous example’ of jus cogens, a qualification later confirmed by the ICJ in Nicaragua. 11 UN Charter. Chapter VII, Article 39. Source: http://www.un.org/aboutun/charter/ 12 Ibid. Article 42.



Although not a judicial organ,13 a determination by the Council is conclusive “despite any

misgivings that they may entertain concerning the merits of the case”.14

With regards to unilateral action, self-defence is the only exception to Article 2(4) available

to States under the UN Charter, and (as is generally understood by most scholars and –most

importantly- States15) customary law as well. It is found in Article 51 of the UN Charter, and

was drafted in conditional form: “Nothing in the present Charter shall impair the inherent

right of individual or collective self-defence if an armed attack occurs against a Member of

the United Nations […]”16

Such conditional (if A then B) wording has created general controversy as to what extent

Article 51 codified pre-existent customary law on self-defence, thus restricting the right to

self-defence to a literal reading, and how much of it has remained outside the specifications

of the Charter.

The latter approach bases its case in a two-tiered argument: first, that the Charter, through

its reference to States’ ‘inherent’ right, actually preserved previous customary law, not

replacing it. This was agreed by the International Court of Justice in its ruling on the

Nicaragua case, when it argued that “the UN Charter by no means covers the whole area of

the regulation of the use of force in international relations”, such as the principles of

necessity and proportionality, and “cannot therefore be held that Article 51 is a provision

which ‘subsumes and supervenes’ customary international law; it rather demonstrates that

custom continues to exist alongside treaty law”.17

Secondly, that such customary law, at the time of the drafting of the Charter, did not restrict

itself to the parameters of Article 51, but did allow force, for example, for the protection of

13 It is composed of 15 members, 10 non-permanent, 5 permanent and its decisions are bound to reflect political rather than strictly legal considerations. 14 Dinstein, supra note 1. 15 As it was discussed above, States acting unilaterally have been reluctant to justify actions that were not in accordance with Article 2(4) in any terms other than self-defence and Article 51. 16 UN Charter. Article 51. Source: http://www.un.org/aboutun/charter/ 17 ICJ Summary of Judgment. Military and Paramilitary Activities in and against Nicaragua (Nicaragua vs. United States of America). Source: http://www.icj-cij.org/docket/index.php?sum=367&code=nus&p1=3&p2=3&case=70&k=66&p3=5



nationals abroad, in anticipatory self-defence or intervention with the consent of the

territorial State, armed reprisals and use of force to stop atrocities.18

With regards to the literal approach, supporters reject that custom allowed for different

justifications to use force at the time the Charter was drafted.19 In their view, the right of a

State to self-defence arises if and only if an armed attack occurs against such State. The right

must be seen as a specific exception to the general prohibition set in Article 2(4), and

therefore naturally restricted to a specific set of conditions. If a wider customary right to

self-defence had survived the Charter unfettered by these restrictions, Article 51 would, in

effect, have been meaningless since its drafting.

At any rate, as was the case with Article 2(4), the debate is mostly academic. Inter-State

discourse – and even States dealing with non-state actors, have showed that “in practice,

States making their claims to self-defence try to put forward arguments that will avoid

doctrinal controversy and appeal to the widest possible range of States”.20

The general paradigm is based on three components: first, the occurrence of an armed

attack; after which the right to self-defence by means of military force is triggered on the

victim State; and the two parameters under which this defence may be exerted, which are

necessity and proportionality.

The concept o f armed at tack Even when it’s the only universally recognized triggering factor for self-defence, neither the

Charter nor any official text provide with a definition of armed attack. The concept is based

on four aspects: the scale of force used, the intention behind its use, the perpetrator and its

starting point. As will become clear later, some of these acquire particular relevance when

dealing with inter-State self-defence, while others generate a more in depth discussion when

referring to armed attacks committed by non-state actors.

18 Cassese, Antonio. International Law. Oxford University Press. 2005. Page 354. 19 Dinstein, supra note 1, doubts there is any evidence in the practice of States to affirm customary law allowed for other forms of self-defence. 20 Gray, Christine. International Law and the Use of force. Oxford University Press. 2004. Page 99.



With regards to the amount of military force, the “generally accepted standard is that… the

aggression must be by armed force and of sufficient magnitude and severity.”21 The

vagueness of this definition, according to some authors, leaves the final determination to the

criteria of the victim State, albeit subject to legal scrutiny a posteriori by the international

community. Other authors prefer the 1974 General Assembly resolution on the Definition

of Aggression as indicative of “widely accepted acts that have been labelled armed attacks”,22

as are invasion, bombardment and placing territory at another State’s disposal. This was also

the International Court of Justice’s position when dealing with the definition of armed attack

in Nicaragua.23 And still a third group of scholars, particularly from the UK, believe “an

armed attack means any use of armed force, and does not need to cross some threshold of

intensity. Any requirement that a use of force must attain a certain gravity and that frontier

incidents, for example, are excluded is relevant only in so far as the minor nature of an attack

is prima facie evidence of absence of intention”.24

The intention behind the armed attack is much less controversial. The ICJ tackled the issue

directly when dealing with the Iranian Oil Platforms case, brought to the Court by Iran against

the US. While discussing whether the US had suffered an armed attack when one of its

warships was struck by a mine set in international waters, the Court ruled that although it did

not “exclude the possibility that the mining of a single military vessel might be sufficient to

bring into play the ‘inherent right of self-defence’”,25 it was impossible to conclude from the

evidence provided that the mine-laying had the specific intention of harming a US vessel.

Scholars have been cautious not to suggest that military attacks on a State carried out

indiscriminately would not trigger self-defence, though this has also been criticised as not

supported by international law.26

21 Printer Jr, Norman. The Use of force against non-state actors under International Law: An Analysis of the US Predator Strike in Yemen. UCLA Journal of International Law & Foreign Affairs. 2003. Page 338 22 Guruli, Erin L. The terrorism era: Should the International Community redefine its legal standards on use of force in self-defence? Willamette Journal of International Law & Dispute Resolution. Volume 12. 2004. Page 102. 23 For a detailed analysis of what the Court ruled regarding use of force short of an armed attack (self-defence vs. armed attack; counter-measures vs. forcible measures), see Dinstein supra note 1. Page 194. 24 Wilmshurst, Elizabeth. Principles of International Law on the Use of Force by States in Self-defence. Chatham House International Law Programme. October 2005. Source: http://www.chathamhouse.org.uk/index.php?id=79 25 ICJ Summary of Judgment. Oil platforms (Islamic Republic of Iran vs. United States of America). Source: http://www.icj-cij.org/docket/index.php?sum=634&code=op&p1=3&p2=3&case=90&k=0a&p3=5 26 Wilmshurst. Supra note 24.



Thirdly, the concept of “armed attack” has been discussed from the point of view of the

perpetrators. Armed attacks carried out by the military of another State need little

consideration. Yet the employment of irregular forces, or their effective control (financially

or operationally) by a State in order to attack another State has been extensively discussed

and has now become of paramount importance, as victim States struggle to attach

responsibility to other States for attacks perpetrated by non-State actors. With regards only

to inter-State use of force, it is sufficient to quote the ICJ in Nicaragua, where it was

determined that “an armed attack must be understood as including not merely action by

regular armed forces across an international border, but also the sending by or on behalf of a

State of armed bands, groups, irregulars or mercenaries, which carry out acts of armed force

against another State of such gravity as to amount to, inter alia, an actual armed attack

conducted by regular forces”.27

Finally, interest in when an armed attack can be considered to have begun is also of crucial

importance, as “verification of the precise instant at which an armed attack commences is

well-nigh equivalent to an identification of the aggressor and the victim State respectively”28;

and once this is achieved, so is the moment in which the victim State can allege to use force

in self-defence. What concrete State action should be used to pinpoint this ‘instant’,

however, is hard to determine.

The simplest solution to the problem would be to establish which State fired the ‘first shot’.

Yet the criteria can face difficulties from three fronts: first, when States conducting an armed

attack need not fire any shots. This was the case in 1999, when Pakistani troops moved into

Indian Kashmir, into a tract of land not easily accessible to Indian authorities. Pakistan was

able to invade India without facing any resistance. When Indian troops moved into the area

and confronted the invading forces, they acted in legitimate self-defence against a shot-less

armed attack.

Second, when the “first shot” needs not reach its target. During the Cold War, both the US

and the USSR had mechanisms to detect enemy missiles being launched, and could then take

27 ICJ Summary of Judgment. Supra note 17. 28 Dinstein. Supra note 1. Page 188.



military action before being hit. In such scenario, “once a button is pressed, or a trigger is

pulled, the act is complete (while impact is a mere technicality).”29

A third situation contemplates a case in which, thanks to military intelligence or otherwise,

the victim State finds out of the preparations being carried out by other States in order to

attack it. The missiles have not yet been launched, yet the information in possession of the

victim State says they will be. Should the victim State wait for the ‘pressing of the button’ in

order to defend itself? Even scholars that reject a wide approach to the Charter’s provision

on self-defence acknowledge that, in these cases, “the crux of the issue is not who fired the

first shot but who embarked upon an apparently irreversible course of action, thereby

crossing the legal Rubicon. The casting of the die, rather than the actual opening of fire, is

what starts the armed attack”.30

This notion is known as ‘anticipatory self-defence’ and is by no means innovative nor lacks

criticisms. It has its roots in the famous and often-quoted Caroline case, settled in 1841

(almost a century before the Charter) and most particularly in the resulting criterion of

‘imminence'. The principle is simple: force may be used only when any further delay would

result in an inability by the threatened State effectively to defend against or avert the attack

against it.31 As was stated by the United Nations Secretary-General Kofi Annan, in his report

“In Larger Freedom”, it is this ‘circumstance of irreversible emergency’ what makes this resort

to force be considered “fully covered by Article 51, which safeguards the inherent right of

sovereign States to defend themselves against armed attack. Lawyers have long recognised

that this covers an imminent attack as well as one that has already happened”.32

Though definitely crucial when discussing self-defence against non-State actors, ‘anticipatory

self-defence’ has been rarely invoked by States against States. As Gray explains, they “clearly

prefer to rely on self-defence in response to an [actual] armed attack if they possibly can… It

29 Ibid. Page 190 30 Idem. 31 Green, James. Docking the Caroline: Understanding the relevance of the formula in contemporary customary international law concerning self-defence. Cardozo Journal of International and Comparative Law. Volume 14. 2006. Page 433. 32 Annan, Kofi. In Larger Freedom. Report of the Secretary General to the General Assembly, 59th Session. 21st March 2005. Paragraph 124. Source: http://daccessdds.un.org/doc/UNDOC/GEN/N05/270/78/PDF/N0527078.pdf



is only where no conceivable case can be made that there has been an armed attack that they

resort to anticipatory self-defence. This reluctance expressly to invoke anticipatory self-

defence is in itself a clear indication of the doubtful status of this justification for the use of

force”.33

Necess it y and proport ional i t y Webster’s famous correspondence related to the Caroline is also considered a touchstone for

the parameters by which, once an armed attack has occurred, use of force in self-defence can

be lawfully carried out.34 These parameters are based on the notions of necessity and

proportionality, and are widely accepted as ‘inherent in the very concept of self-defence’ and

thus part of customary international law.35

The necessity requirement must be fulfilled on two levels: firstly, for a victim State to resort

to force, it must be clear that the armed attack cannot be effectively countered by measures

not involving the use of force or by military operations on a lesser scale. In other words, an

attacked State can only resort to force if it reasonably believes it is the only option available

to confront the enemy. As Robert Ago states, “had a State been able to achieve the same

result by measures not involving the use of armed force, it would have no justification for

adopting conduct which contravened the general prohibition against the use of armed

force”.36

The second level is triggered once use of force is the chosen option, and remains active

throughout the duration of the military operation being carried out in self-defence. Again, it

imposes limitations on the use of force the victim State may use against the aggressor. The

principle is that “by limiting the use of force to circumstances only when necessary, it

follows that once military operations have been initiated, they must cease when an enemy is

defeated or no longer has the means to fight. In that sense, the concept of necessity 33 Gray, supra note 20. Page 130. 34 “The action must not be unreasonable or excessive, since the act, justified by the necessity of self-defence, must be limited by that necessity and kept clearly within it”. Letter from Daniel Webster, US Secretary of State, to Lord Ashburton, British Special Representative to the US. Green, Supra note 31 35 The ICJ consistently applies them as part of its analysis in cases concerning use of military force. See Nicaragua, Oil Platforms, and the advisory opinion on the Use or threat of Nuclear Weapons. 36 Ago, Roberto. Addendum. Eight report on State responsibility by Mr. Roberto Ago, Special Rapporteur – the internationally wrongful act of the State, source of international responsibility (part 1). Extract from the Yearbook of the International Law Commission. Volume II. 1980. Page 69.



effectively imposes a cap on the lawful period of hostilities”.37 As will be discussed later, this

clear-cut definition of the concept of necessity turns messy when dealing with non-state

actors, as such conditions as the defeat of the enemy or the elimination of the threat of

further attacks are particularly hard to establish.

Closely related to the principle of necessity is the concept of proportionality, considered by

some authors as the essence of self-defence.38 More loose a term than the concept of

necessity, it also demands to be constantly considered as long as force is being used, as to

keep in focus the same (and only) purpose: that of halting and repelling the armed attack.

For a use of force to be proportionate, there must be “some symmetry between the initial

use of unlawful force and the responsive counter force, based upon the gravity of the

preliminary attack and the continuing threat posed by the enemy”.39 Some authors have

extended this to mean that the physical and economic consequences of the force used, and

not only the force itself, should not be excessive in relation to the harm expected from the

armed attack.40 However, because a State would have no way to know for certain what

amount of counter force it would require to defeat the aggressor, it is generally accepted that

the principle can be applied with certain degree of flexibility. What remains clear is that there

is no need to search for strict proportionality between the conduct constituting the armed

attack and the opposing conduct. “The action needed to halt and repulse the attack may well

have to assume dimensions disproportionate to those of the attack suffered. What matters in

this respect is the result to be achieved by the defensive action, and not the forms, substance

and strength of the action itself”.41

Summary So far this paper has explored the current law and principles behind inter-State use of force,

with particular emphasis on the self-defence doctrine. This doctrine has been severely

questioned as inappropriate to deal with attacks by non-state actors. In the following

sections, the concepts discussed here will be tested against recent State practice and scholarly

37 Printer. Supra note 21. Page 343. 38 Brownlie, Ian. The Use of force by States in international law. Clarendon Press. 1963. Page 261. 39 Dinstein. Supra note 1. 40 Wilmshurst. Supra note 24. 41 Ago. Supra note 36.



opinions in this regard, particularly concerning how the law applies or should evolve to rise

to the challenge.



Part Two. Resorting to self-defence against non-State actors.

“I think in the war on terrorism there are no rules. They have none and we have to take whatever risks you

have to take to make them fear us” (Former Senator Warren Rudman1)

Part One discussed inter-State use of force and the self-defence doctrine as it is understood

since the drafting of the UN Charter. Although much of its details are still subject to

interpretation and debate, in general terms scholars and States agree on the broad rules that

must be observed: namely, that use of force may only be employed against an armed attack,

and that the response should be limited by what is necessary and proportionate to put an

end to the aggression.

Scholars also tend to agree in that these rules, and particularly those in the UN Charter, were

originally conceived to deal with the use of force by States against States. This situation has

changed dramatically. The destruction of the World Trade Centre and subsequent attacks in

Madrid, London and South East Asia, as well as the war in Afghanistan and Iraq, have

forced States, and consequently scholars, to cease treating terrorist attacks as an exceptional

occurrence (thus a minor challenge, if at all, to the law) and focus their attention in much

more detail to actions of non-State actors and their status under international law. This

section will attempt to address this issue responding to the following questions: can

international law be applied to non-State actors, and if so, to what extent? Similarly, should

States be constrained by the rules of self-defence when dealing with non-States? This

analysis will next narrow its focus to the legal nature of an armed attack perpetrated by non-

State actors, with the intention of establishing whether it can, too, trigger Article 51 and the

laws of self-defence. The debate will centre on three aspects: the scale of the attack, the

perpetrator, and finally State practice and the possibility of creating instant customary law.

Non-State ac tors and in ternat ional law Strictly speaking, non-State actors are not bound by the UN Charter or subject to any

provisions involving the use of force. It is doubtful even customary international law – the

1 The Washington Post, 6th November 2002. Source: http://pqasb.pqarchiver.com/washingtonpost/search.html



result of State practice and opinio juris – could be applied to them. This argument finds

support in the Charter’s prohibitive language of Article 2(4), where it states “all Members shall

refrain… from the threat or use of force” (emphasis added), not mentioning other

international persons and as such restricting the general prohibition to the States members

of the UN. Following the position that Article 51 must be understood in conjunction with

Article 2(4), an approach discussed in Part One, it would be logical to assume all provisions

on use of force found in the Charter are directed toward States exclusively, even if other

provisions have no such limiting wording. Similarly, as treaties are typically concluded

between two or more States, the Charter’s status as a treaty means it can only bind States qua

States. For these reasons, and “to the extent that these points are technically correct, a

terrorist organization, as a non-State entity, cannot be bound by the Charter as a matter of

conventional law”.2

This literal and perhaps unnecessarily restrictive interpretation of the laws of use of force is

one that scholars and States just briefly acknowledge, at best, and then discard. Consistency

with the importance and extensive attention normally given to the wording in the Charter,

however, should prevent this debate from being ignored. Inclusion of non-State actors under

international law’s binding power has been argued for in the following terms3:

First, an entity that elects to use force on the international plane should be treated as an

international actor and should be bound, therefore, by accepted international norms, in this

case, at least customary international law. Brownlie supports this practical approach to

conferring international status to non-State actors: “International lawyers cannot afford to

ignore entities which maintain some sort of existence on the international plane in spite of

their anomalous character. Indeed, the role played by politically active entities such as

belligerent communities indicates that, in the sphere of personality, effectiveness is an

influential principle”.4 The argument is also compelling in that it turns the attention onto the

non-State actors, as it presents upon them the syllogism: Entities that act in the international

sphere are bound by international law; these have traditionally been States; if any other

2 Printer, Norman. The Use of force against Non-State actors in International Law: An analysis of the US Predator strike in Yemen. UCLA Journal of International Law & Foreign Affairs. 2003. Page 345 3 Printer. Supra note 2. 4 Brownlie, Ian. Principles of Public International Law. Oxford University Press. 5th Edition, 1998. Page 64.



person wants to act in the international scene, then inevitably it will be bound by the

international rules of the game.

Similarly, excluding non-State actors from the application of the norms of the Charter would

be inconsistent with the very purposes of the United Nations, namely, the maintenance of

international peace and security. As Printer suggests, “the Charter’s principles would be ill-

served if the activities of rogue groups fell outside the document’s norms. A non-State entity

that uses deadly force on a global scale can just as easily threaten peace and security as a

State can”,5 if not more.

Thirdly, the capacity to include non-State actors (private entities) within the applicability of

public law finds jurisprudence in the Nuremberg trials after the Second World War and the

posterior development of human rights and international criminal law. Then as now, the law

evolved to account for the violation of norms by previously unrecognized subjects of

international law, namely criminally responsible individuals. It is now accepted that “matters

that were once thought to be issues solely between State actors have devolved to affect

private entities and private persons”.6 Just as NGOs (who do not typically enjoy

international legal personality) have been increasingly recognized as subjects of international

law with some incidents of legal status, so non-State actors with illegal objectives should not

be restricted from possessing similar ones if the consequence is to enhance their

accountability under international law.

This argument appeals to the subtle differences between Charter and customary norms. As it

was discussed in Part One, it is widely recognised that both these bodies of law do not

exactly match, a view shared by the International Court of Justice in Nicaragua. As such, even

if Article 51 were to be interpreted under the scope of the general prohibition in Article 2(4),

it would still be possible to argue that the existence of an ‘inherent right of self-defence’,

which exists independently of the Charter, would still provide States the right to defend

themselves against armed attacks perpetrated by international entities other than UN

members. The famous Caroline case, already mentioned, provides a perfect precedent.

5 Printer. Supra note 2. 6 Idem.



Complementing these ideas, it would be possible to add that, even if non-State actors were

to be considered not bound by the norms of international law, this should not in any way

impair these rules from being accessible to States, who are indeed undoubtedly bound. In

other words, even if non-State actors were to ‘choose’ not to play according to the rules of

the game, once their actions affect a State, nothing in those rules would prohibit States from

reacting and applying them. The only limitation would be that they conduct their response

within the framework of a lawful resort to force, to which they are bound by treaty and

customary law, as has been already discussed.

The ‘armed at tack’ requirement In order for a State to be able to respond within the legal framework, one prerequisite still

holds: that the action perpetrated by the non-State actor amounts to an “armed attack”, in

the terms conceived of in Article 51. This has been thoroughly analysed and discussed by

scholars from two angles: that of the perpetrator, on one hand, and from the nature of the

attack itself, on the other.

The main argument against considering a terrorist attack an “armed attack” falls within the

general interpretation of the UN Charter as a body of norms directed to States exclusively,

which in itself entails that, therefore, the attack has to originate from a State. As Giorgio

Gaja, member of the International Law Commission, explains, “armed attack is a sub-

category of aggression, as explicitly said in the French text of Article 51 of the Charter”, and

as such falls under the definition found in the General Assembly Resolution 3314. As is

mentioned there, an aggression clearly has to come from a State.7 In order for a State to

legally use self-defence, he continues, it is necessary to direct it against the State harbouring

the non-State perpetrators, previously determining what degree of responsibility this State

holds regarding these actors. This debate will be addressed in Part Three of this paper.

Furthermore, the above interpretation seems to have been the chosen one by the ICJ in its

dealing with the Advisory Opinion Legal Consequences of the Construction of a Wall in the Occupied

7 Gaja, Giorgio. In what sense was there an “Armed attack”? The Attack on the World Trade Centre: Legal Responses. European Journal of International Law, Online Discussion Panel. Source: http://www.ejil.org/forum_WTC/ny-gaja.html



Palestinian Territory, a case published two years after the September 11th events. After Israel

argued for the construction of the Barrier as consistent with Article 51 of the Charter and its

inherent right of self-defence, the Court re-examined the current state of the laws and

succinctly concluded that “Article 51 of the Charter thus recognises the existence of an

inherent right of self-defence in the case of an armed attack by one State against another

State”8 (emphasis added).

The above arguments are not widely accepted. With regards to the necessary involvement of

a State to qualify non-State action as an “armed attack”, Guruli first quotes the Vienna

Convention on the Law of Treaties, where it’s stated that “a treaty shall be interpreted in

good faith in accordance with the ordinary meaning to be given to the terms of the treaty”.9

Even if the drafters of the UN Charter did not envision an entity other than a State carrying

out an armed attack, this cannot, however, be granted more importance than a literal reading

of the article. As is well known, Article 51, unlike 2(4), makes no mention of who should

perform the armed attack in order to trigger the right of States to self-defence.

This is consistent with the generally accepted notion of what is deemed to be pre-Charter

customary self-defence, already discussed above. Murphy explains it best: “The pre-eminent

precedent regarding self-defence – the 1847 Caroline incident – stands not just for Secretary

of State Webster’s proposition that self-defence is only appropriate in cases of necessity…

but also for the proposition that self-defence is permissible as a reaction to attacks by non-

governmental entities (in that case, support by US nationals for a rebellion in Canada)”. To

the extent that Article 51 preserves States’ ‘inherent’ right of self-defence prior to the UN

Charter, it included the right to respond to attacks regardless of the source.10

Concerning the ICJ advisory opinion, scholars’ critiques have ranged from simple regret for

the language used to elaborate interpretations of the Court’s ‘true intentions’. In the opinion

of Philippe Sands, for example, the Court failed “to take into account developments across

8 ICJ Advisory Opinion Legal Consequences of the Construction of a Wall in the Occupied Palestinian Territory. Paragraph 138. Source: http://www.icj-cij.org/docket/index.php?p1=3&p2=4&code=mwp&case=131&k=5a 9 Vienna Convention on the Law of Treaties, UNTS, 1969. Article 31. 10 Murphy, Sean. Terrorism and the concept of “armed attack” in Article 51 of the UN Charter. Harvard International Law Journal. Volume 43. 2002. Page 50.



the world, in particular a rise of non-State organizations which are committed to terrorist

activities, an increase in the number of ‘failed States’, and the dangers posed by the

proliferation of weapons of mass destruction”.11 Similarly, Sir Adam Roberts lamented the

Opinion would “likely reinforce concerns that the ICJ is not as rigorous as it should be; and

that is not knowledgeable about security issues”.12 Eick, less critical, believes the Court

merely reflected the obvious point that unless an attack on a State is directed from outside

that State’s territory, the question of self-defence does not rise, thus not really reflecting on

the perpetrator of the armed attack (State or non-State), but rather on the ‘territorial origin’

of such attack (outside the victim State’s territory). It should be noted that Judge Higgins, in

her dissenting opinion, argued that “there is, with respect, nothing in the text of Article 51

that thus stipulates that self-defence is available only when an armed attack is made by a

State”.13

A second approach to analysing whether attacks perpetrated by non-State actors may equate

to “armed attacks” is by focusing on their nature. To do this, several scholars employ a

continuum to differentiate the various types of incidents involving non-State acts. At the low

end of the scale are such actions as the provision of arms to nationals who are seeking to

overthrow their own government. This would not amount to an armed attack but rather to a

criminal offence. At the high end of the scale, on the other hand, there would be actions

such as armies crossing borders, as well as a State sending armed irregulars who ‘carry out

acts of armed force against another State of such sufficient gravity as to amount to an actual

armed attack by regular forces’.

Within this framework, some have argued the attack on the World Trade Centre in 2001

would fall on the low end of the scale, as the hijackers were not an organized armed band as

such. They were a “small group of persons, who did not in any sense operate as normal

military or paramilitary units, and who were engaged in isolated incidents”.14 They were

11 Wilmshurst, Elizabeth. Principles of International Law on the Use of Force by States in Self-defence. Chatham House International Law Programme. October 2005. Source: http://www.chathamhouse.org.uk/index.php?id=79 12 Idem. 13 Higgins, Rosalyn. Dissenting Opinion for the ICJ Advisory Opinion Legal Consequences of the Construction of a Wall in the Occupied Palestinian Territory. Source: http://www.icj-cij.org/docket/files/131/1681.pdf 14 Murphy, S. Terrorism and the Concept of Armed Attack. Harvard International Law Journal. Volume 43, Number 1. 2002. Page 45.



armed with nothing more than small knives. If necessary to compare them with “regular

forces”, as Nicaragua would suggest, it would be easier to conclude they did not engage in an

armed attack in any conventional sense. This was suggested by Murphy, who argued that

September 11th “would perhaps be better characterized as a conventional (albeit heinous)

criminal act”.15 He finds support for his argument in the fact that various conventions aimed

at dealing with terrorist acts, such as hijacking of aircraft and attacks against State facilities

using explosive devices, regard these actions as criminal offences, with the purpose of

submitting offenders to prosecution. This would also seem to have been the General

Assembly’s position when it called for “international cooperation to bring to justice the

perpetrators, organizers and sponsors”16 of the incidents.

In similar terms, Guruli divides non-State acts into three categories: criminal acts, at the base

of the pyramid, followed by terrorist acts in the middle level, and “armed attacks” at the top.

In such a model, every terrorist act is a criminal act, but not every criminal act is a terrorist

act. Logically, a criminal act must possess certain characteristics to rise to the level of

terrorist act, and then fulfil other prerequisites to be considered an “armed attack”. These

have been discussed from various angles: the perpetrator (already discussed), the weapons

and methods of force used, the gravity of the attack, its location, past incidents (or context),

the national reaction and the international reaction.

With regards to the employment of certain weapons, one of the main developments of the

current struggle against non-State actors is their access to modern technological

advancements, and most particularly weapons capable of maximizing the death toll. This has

recently become apparent after information was gathered regarding non-State actors’ access

to dirty bombs.17 Similarly, even if Iraq’s infamous weapons of mass destruction proved to

be fictitious, the argument was used by President Bush to justify US use of force: “Imagine

those 19 hijackers with other weapons and other plans -- this time armed by Saddam

15 Ibid. Page 46. 16 General Assembly Resolution. 56th Session, Resolution 1, 2001. Source: http://daccessdds.un.org/doc/UNDOC/GEN/N01/475/00/PDF/N0147500.pdf 17 Council on Foreign Relations. Backgrounder, Dirty bombs. Source: http://www.cfr.org/publication/9548/



Hussein. It would take one vial, one canister, one crate slipped into this country to bring a

day of horror like none we have ever known”.18

Though the employment of WMD or dirty bombs would certainly help the act be

considered an armed attack on a State, the criterion should not be considered outcome

determinative on its own. As was already mentioned, the 9/11 hijackers used no more than

pocket-knives to surrender the crew, and then turned commercial aeroplanes into projectiles.

Surely none of the materials used in such action could a priori be considered enough proof to

classify it as an Article 51 “armed attack”.

The gravity of the attack, measured in terms of its consequences, can also provide useful

insight into its classification as an “armed attack”. These consequences are usually measured

in terms of fatalities and economic losses. Regarding the former, it is widely acknowledged

that on 9/11, the 5,000 plus people dead, from 81 different nationalities, definitely “tilted

perceptions, both domestic and international, toward the view that the acts were more likely

than not, armed attacks”.19 Yet, it would be unnecessarily restricting to reduce an “armed

attack” to the number of people dead. As was mentioned in Part One, shot-less armed

attacks have and still occur. Secondly, the targeted State may be capable of minimising the

attack’s impact, a situation that should not benefit the aggressor in terms of limiting the

victim State’s possibility to label the aggression an armed attack and thus trigger its own

defence.

As to the economic effects of the attack, it would be impossible to ignore its contribution to

the general impact on the victim State and the international community as a whole. Even

Osama bin Laden assessed 9/11 calculating the US’ economic losses.20 Yet it should also be

noted that many factors contribute to making the very same terrorist act more or less

economically devastating. “Like the number of fatalities, it may depend on the country’s

18 Bush, George W. State of the Union Address. 28th January 2003. Source: http://www.whitehouse.gov/news/releases/2003/01/20030128-19.html 19 Guruli, Erin L. The terrorism era: Should the International Community redefine its legal standards on use of force in self-defence? Willamette Journal of International Law & Dispute Resolution. Volume 12. 2004. Page 111. 20 Lawrence, Bruce. Messages to the World: the Statements of Osama Bin Laden. Verso, 2005. Page 111.



reaction and its ability to minimize economic damage. Unlike fatalities, however, the actual

economic damage might not be ascertained for years later”.21

Most terrorist attacks have not and will not be of the scale and impact of 9/11. As it has

been the case for Israel and the US, most non-State acts of violence are relatively minor

incidents,22 “not the type of massive attack by military forces which the drafters

envisioned”.23 For such reason, some scholars propose the fact that an “armed attack” may

constitute an accumulation of minor events, rather than one single operation. Blum agrees:

“The extent of terrorist activity is relevant in assessing the plea of self-defence… Each of the

acts of terrorism, when viewed separately, might not qualify as an armed attack, but the

totality of such acts may reveal such a pattern”.24 German international lawyers have called

this approach Nadelstichtaktik (needle prick tactics), holding that while each needle prick in

itself might not cause any pain, the overall effect of many needle pricks may amount to

serious, intolerable harm.

The location of the terrorist attack is also an important factor of analysis. There has been

extensive discussion on the legality of a State taking action against an attack on its nationals

abroad. While some scholars affirm certain attacks on civilians could constitute an “armed

attack” against the State,25 others have difficulties accepting this could occur even when

directed against appointed representatives of such State, i.e. diplomats or other public

officials.26 A third group adds to the debate advocating for the proposition that attacks on

nationals may be considered an armed attack only if the host State is unable or unwilling to

protect them.27 A combination of all is probably the most appropriate position. “When

threats are directed against nationals solely because of association with the targeted State and

21 Guruli. Supra note 19. Page 112 22 From 1975 to 1985, for example, more than 5,000 ‘terrorist incidents’ were reported worldwide. Of course the current number can be calculated in the thousands per year. Source: Arend, Anthony & Beck, Robert. International law and the use of force. Routledge Eds. 1993. Page 139 23 Baker, Mark. Terrorism and the Inherent Right of Self-defence. (A call to Amend Article 51 of the United Nations Charter). Houston Journal of International Law. Volume 10. 1987. Page 38. 24 Blum, Yahuda. The Beirut Raid and the International Double Standard; A reply to Professor Richard A. Falk. American Journal of International Law. Volume 80, 1970. Page 136. 25 Guruli. Supra note 21. Page 112. 26 For example, professor Francis Boyle. Boyle, F. Remarks, Proceedings American Society of International Law, 1987. 27 Schachter, Oscar. The Lawful Resort to Unilateral Use of Force. Yale Journal of International Law. 10. Page 292.



the threats are serious and substantial, with the host State unwilling to protect the targeted

nationals, the ultimate outcome should not rest upon their official or unofficial capacity”.28

Of course, the case of an attack on the territory of a State, originated in another State, needs

little discussion.

The non-State actor’s attack on the State may also be observed from the point of view of

domestic reaction to the event. After 9/11, the US immediately perceived the incidents as

akin to that of a military attack. President Bush labelled it an “act of war”, declared a national

emergency and called to active duty the reserves of the US armed forces. A week later, the

US Congress adopted a joint resolution authorizing the President to use ‘all necessary and

appropriate force” against those responsible. When addressing the Security Council, the US

reported to have been the victim of an armed attack by Al Qaeda and would respond in self-

defence. All these actions taken after the destruction of the WTC have been described by

Murphy as “convincing arguments that the 9/11 incidents constitute an ‘armed attack’

against the United States”.29

Yet the domestic reaction will always pose problems when attempting to reach an objective

evaluation of what constitutes such an attack by a non-State actor. First, it can immediately

be assumed that the domestic reaction to an attack will always be construed to fit the victim

State’s best interests (be it in preparation for its reaction or to appease the Government’s

constituents). Similarly, since in most cases it is left to the victim State to determine the

nature of the attack suffered, it is likely that it be abused by those States willing to use force,

either in retaliation or self-defence.

Finally, the reaction of the international community, be it through multilateral organizations

or through State practice, can also serve to classify an attack. As will be seen later, this is

particularly relevant if the reaction comes in the form of a Security Council resolution

authorizing the use of force. Again it should be noted, however, that a lack of international

approval does not automatically disqualify the incident. Though entrusted with the

maintenance of international peace and security, the Security Council has a very particular

28 Guruli. Supra note 21. Page 112. 29 Murphy. Supra note 14. Page 48.



decision-making process: many resolutions are the result of complex and very politically-

oriented negotiations rather than an objective evaluation of facts and law, and many times

determined by the use or threat of use of any of the permanent five members’ veto power.

It is neither possible nor necessary to determine what importance should be given to the

above-mentioned factors in order to establish whether a State can claim being a victim of an

armed attack, and thus trigger its defence. All of them pose advantages as much as individual

problems and have been used extensively by States in order to justify their actions. This State

practice will be analysed below, including the current state of affairs post-September 11th and

the possibility of new instant custom arising from the international community’s reaction to

the event.

State prac t i c e and opinio juris Though terrorism is by no means a recent phenomenon, the practice of States arguing self-

defence in order to justify their use of force is limited to no more than a handful of cases, all

of which have involved Israel or the US.

The first instance was the attack by the Israeli air force on the Beirut airport, in response to

an earlier attack on an Israeli commercial plane in Athens. The case, already described in the

Introduction to this paper, received a unanimous condemnation from the Security Council.

Back in 1968, only the US accepted the argument that self-defence could be triggered by a

terrorist attack. In this particular case, however, it made a point of explaining that the

reaction had been unlawful because Lebanon, as such, had not been responsible for the

attack in Greece.30

Israel encountered the same reaction by the Security Council five years later, after Israeli

aircraft intercepted a Middle East Airlines flight en route from Beirut to Baghdad, forcing

the plane to land in an Israeli military base. Though the crew and passengers were subject to

intense questioning, no further military force was used. Israel justified its actions as self-

defence to the Security Council, but this time even the US expressed its disapproval. Its

position is worth noting: according to US Ambassador John Scali “the commitment to the

30 Gray, Christine. International Law and the Use of force. Oxford University Press. 2004. Page 161.



rule of law in international affairs… imposes certain restraints on the methods Governments

can use to protect themselves against those who operate outside the law… The United

States government believes actions such as Israel’s diversion of a civil airliner… are

unjustified and likely to bring about counter-action on an increasing scale”.31

In 1985, Israel launched an air strike on the Palestinian Liberation Organization headquarters

in Tunis, as a response to the murder of three Israelis in Cyprus a week before. During the

Security Council debates, Israel maintained Tunisia had allowed its territory to be employed

by terrorist organizations, exposing itself to become a legitimate target of self-defence. The

Council, once more, disregarded Israel’s concept of “armed attack”, labelled its actions as an

“active armed aggression” and urged it to “refrain from perpetrating such acts or from

threatening to do so”.32 The US, though abstained, argued through its Ambassador Vernon

Walters that it “recognized and strongly supported the principle that a State subjected to

continuing terrorist attacks may respond with appropriate use of force to defend itself

against further attacks”, a course of action which he identified as “an aspect of the inherent

right of self-defence recognized in the UN Charter”.33

This outright rejection of the use of military force against terrorist actions in self-defence

begun to shift in 1986, after the US attacked targets in Tripoli in response to attacks on its

nationals in a discothèque in Munich. The US informed the Security Council it was acting in

self-defence in response to past terrorist attacks and also to deter similar attacks in the

future. Though most States condemned the operation, this time the United Kingdom and

France joined the US in vetoing the resulting resolution, joined by Denmark and Australia,

while Venezuela abstained. This trend found confirmation in 1993, after the alleged

assassination attempt against former US president Bush Sr. The US again claimed self-

defence after firing missiles at the Iraqi Intelligence Headquarters in Baghdad, the prime

suspects. For the first time, the response of the Council showed considerable sympathy with

the justification; according to some scholars, it is this case that may have “marked the

31 Security Council S/PV Meeting Records, cited in Arend, Anthony & Beck, Robert. International law and the use of force. Routledge Eds. 1993. Page 149 32 Security Council Resolution 573. Source: http://daccessdds.un.org/doc/RESOLUTION/GEN/NR0/489/10/IMG/NR048910.pdf 33 Security Council S/PV Meeting Records, cited in supra note 30. Page 153.



emergence of a new rule of international law allowing such actions [self-defence] in response

to terrorism”.34 By 1998, when the US responded to the bombing of its embassies in Kenya

and Tanzania with missile attacks on a training camp in Afghanistan and a pharmaceutical

plant in Sudan, the response of the rest of the world was generally muted.

Though careful not to mistake ‘sympathy and understanding’ with acceptance of a legal

doctrine, State practice up to September 11th 2001 discussed so far would seem to show a

certain pattern of evolution with regards to the international community’s perception of

non-State actors, their role as international actors and their capability of perpetrating “armed

attacks”. This trend received a dramatic push forward after the attacks in New York.

The Security Council’s response on 12th September 2001 showed a unanimous will, for the

first time, to accept the legality of action in self-defence in response to terrorist attacks. All

members passed Resolution 1368, asserting to ‘combat threats to international peace and

security caused by terrorist acts’ and ‘recognizing the inherent right of individual and

collective self-defence in accordance with Article 51 of the Charter’.35 Operation Enduring

Freedom, though not carried out under UN auspices, received the approval of the

international community.

This has been interpreted in various ways: some scholars saw States’ responses as a

confirmation of an already existing legal truth; others argued Article 51 had been drastically

re-interpreted to accommodate States’ responses to deal with global terrorism, allowing them

to respond with force to any non-State act of aggression. This was taken to the extreme of

asserting that 9/11 had created ‘instant customary law’, comparable to that experienced

when banning piracy or during the drafting of the Law of the Sea. As Dinstein wrote, “all

lingering doubts on [admitting non-State actors’ acts as armed attacks] have been dispelled as

a result of the response of the international community to the shocking events of 9/11”.36

The North Atlantic Council’s decision to consider the attack as an “armed attack against one

34 Gray. Supra note 30. 35 UNSCOR 1368. Source: http://daccessdds.un.org/doc/UNDOC/GEN/N01/533/82/PDF/N0153382.pdf 36 Dinstein, Yoram. War, Aggression and Self-defence. Cambridge University Press. Fourth Edition. 2005. Page 208.



or more of the Allies in Europe or North America”,37 plus the 2001 Meeting of Ministers of

Foreign Affairs resolution that “these terrorist attacks against the US are attacks against all

American States”,38 would seem to corroborate this position.

Yet others believe this may have proved to be an over-enthusiastic view of events. True, the

international community’s response provided grounds for the use of force in Afghanistan.

But as Gray would seem to suggest, this precedent could be, in fact, extremely restricted: it

would only apply to “a situation where there had been an actual massive terrorist attack on a

State’s territory, where there was a continuing threat of global terrorism from those

responsible; and where the response was directed against the organization directly

responsible in a State which had allowed it to operate and which then refused to expel it; and

then only after the Security Council had determined the existence of a threat to international

peace and security; and where the Security Council had asserted a right of self-defence”. In

other words, it would apply only to allow forceful intervention in Afghanistan, in 2001, after

the destruction of two massive buildings and the deaths of thousands of people.

The truth is, 9/11 has raised at least as many questions regarding use of force in self-defence

as it has supposedly answered. While some scholars still debate over issues such as

anticipatory self-defence, new controversies have arisen, as the legality of pre-emptive force,

or the Bush doctrine, which most scholars consider downright unlawful. Two years later, in

October 2003, Israel responded “in self-defence” after a Palestinian suicide attack in a

restaurant with its deepest raid into Syria since 1973. As happened back then, and even when

argued in terms of the “Global War on Terrorism”, the majority of States in the Security

Council condemned Israel’s actions as a violation of international law. Pakistan accused Tel

Aviv of exploiting the campaign against terrorism for other purposes; the US, surprisingly,

limited its reaction to a call for restraint. It should also be noted that further resolutions

condemning terrorist attacks have made no mention of States’ ‘inherent right of self-defence’

(as did Resolution 1373), while still regarding them a threat to international peace and

security. This may be taken as “an indication that the right to use force in self-defence

37 North Atlantic Treaty Organization (NATO): Statement by the North Atlantic Council, 2001. Source: http://www.nato.int/docu/pr/2001/p01-124e.htm 38 Organization of American States (OAS): on Terrorist Threat to the Americas, 2001. Source http://cicte.oas.org/Rev/en/Documents/Resolutions/doc_rc_24_res_1_01_eng.pdf



against past terrorist acts may remain exceptional”, that is, to be applicable in very particular

cases.39

Summary The fact that the self-defence doctrine found in Article 51 of the UN Charter and

complementary customary law were originally conceived to restrict the use of force from and

between States have raised questions regarding their applicability against non-State actors.

Though perhaps technically correct, practicality, alternative yet still literal readings of the law

and State practice should resolve the issue. As extensively touched in this section, the same

could be said for the specific question related to what constitutes an “armed attack”, as the

prerequisite to any act of self-defence, when perpetrated by a non-State actor. Even if

accepted, a priori, that a non-State actor may perpetrate such attack, the present review of the

many factors that can help determine what is and what is not to be considered one, do not

make the quest for a final definition any easier. Yet even when the long-term effects of 9/11

are still to be evaluated, the international community’s response to such a particular event

should at least prove that, in particular circumstances, non-State actors may carry out an

“armed attack” and thus trigger use of force by a State in self-defence.

39 Dinstein. Supra note 36.



Part Three. Responding to an armed attack: non-State actors and State responsibility

“They who invade the territories of others and harm those who have done no wrong,

are both lawless and wicked”. (H.Grotius1)

As described in Part Two, the importance of determining whether an act of aggression from

a non-State actor can be labelled an “armed attack” under international law (as worded in

Article 51 of the UN Charter), lies in its unique capacity to trigger the use of force by States

in legitimate self-defence. The fulfilment of this prerequisite, however, only leads to the next

set of questions: particularly, against whom may a State respond in self-defence after being

attacked by a non-State organization? Who, in the international scene, is liable for the

occurrence of such attack?

In a traditional setting, a State victim of aggression from another State may defend itself by

fighting the invading force or the aggressor’s territory (as long as it meets the requirements

of necessity and proportionality), all within the setting of a continuous, international armed

conflict – as envisioned by the drafters of the UN Charter. “Terrorist groups of global

reach”,2 on the contrary, act completely differently: they don’t seek to conquer territory,

control resources or even further traditional political or ideological purposes.3 Their

operations are sporadic, distant in time and space, and can last no more than a few minutes,4

after which the attackers disappear into other countries, perhaps thousands of miles away,5

or purposefully die in the attack.

1 Grotius, H. De Jure Belli Ac Pacis Libri Tres. Chapter 12. As cited by infra note 7. Page 252. 2 Bush, George W. Address to Joint Session of Congress. In Malzahn, Scott. State Sponsorship and Support of International Terrorism: Customary Norms of State Responsibility. Hastings International and Comparative Law Review. Volume 26. 2002-2003. Page 85 3 Travalio G., & Altenburg J. Terrorism, State Responsibility and the Use of Military Force. Chicago Journal of International Law. Volume 4. No 1. 2003. Page 97. 4 The September 11th attacks, for example, lasted less than an hour to carry out. 5 After 9/11, intelligence agencies revealed the attacks on the World Trade Centre were planned at least 3 years in advance from Germany, by what was then labelled the Hamburg Cell. More information may be found at: http://www.9-11commission.gov/report/911Report_Ch5.htm



The problem can be described simply: States are being subject to armed attacks by non-State

actors in a world geographically and solely comprised of States. As Travalio and Altenburg

describe, “[terrorists] must operate from somewhere. They must store weapons somewhere;

they must train and house their fighters somewhere; they must develop their plans

somewhere; and their leaders must sleep somewhere. These activities must occur on the

territory of some State”.6 Figuratively speaking, terrorists only rise to the level of international

actor when they perpetrate an armed attack, only to disappear again behind the curtain of

States.

The ultimate consequence is that any military response to a terrorist attack, in self-defence or

otherwise, inevitably compromises two (or more) States: the victim, surely, and the State

where the attackers originate, regroup, train and prepare the next attack. The following

section will focus on the international responsibility of a State for the actions of private

actors present in its territory by, first, analysing the body of law relating to attribution of

State responsibility and terrorism as it currently stands, with particular attention to UN texts

and the Draft Articles prepared by the International Law Commission. Secondly, it will

compare the norms and past jurisprudence, the Nicaragua and Hostages cases particularly, with

more current standards defended by scholars and some States. Thirdly, it will describe an

alternative approach to determining State responsibility, by which different degrees of State

involvement allow for different responses from the ‘victim’ State, some of them excluding

use of force. This will lead to a final review of the situation by which a link between non-

State actors and a ‘host’ State may be impossible to be established.

State re sponsibi l i t y for non-State ac tions As it was established in Part One, use of force between States is generally prohibited by

Article 2(4) and customary international law. This creates the awkward situation by which

the legal resort to self-defence after an armed attack by a non-State actor would still, in

principle, violate ‘the territorial integrity and political independence’ of the State where non-

State actors are located. The solution to this legal entanglement, as proposed by victim States

and scholars, has been consistent over the years: to attribute the actions of non-State actors

to the State in which they operate. This has been argued from various angles.

6 Travalio et al. Supra note 3.



The first of these refers to the UN and its Charter. As is stated in its Article 1, paragraph 1,

its main purpose is “to maintain international peace and security, and to that end: to take

effective collective measures for the prevention and removal of threats to the peace, and for

the suppression of acts of aggression[…]”.7 With this alone, it could be argued terrorist

groups present a threat to the peace, as has been consistently established by the Security

Council. Thus, the UN and its members would need to fulfil the purpose, collectively, of taking

effective action for the removal and prevention of these threats.

This argument finds reinforcement in the 1970 Declaration on the Principles of

International Law concerning Friendly Relations and Co-Operation Among States. Besides

adding to the body of relevant texts, this Declaration has acquired special significance as an

authoritative interpretation of the UN Charter – mainly due to the drafting committee’s

mandate to confirm the fundamental principles of international law.8 It reads: “Every State

has the duty to refrain from organizing, instigating, assisting or participating in acts of civil

strife or terrorist acts in another State or acquiescing in organized activities within its

territory[…] Also, no State shall organize, assist, foment, finance, incite or tolerate

subversive, terrorist or armed activities”.9 As is clearly noted, the Declaration imposes a duty

to take positive action, not merely the renunciation of certain activities. For sure, General

Assembly resolutions are not binding on States; however, the Declaration has achieved a

special status,10 leading some scholars to believe that “between the two poles of being a mere

recommendation or a binding statement of legal rules, the Declaration may be closer to the

latter”.11 The fact that it was adopted by consensus provides “soft evidence of the opinio juris

of States, especially when passed with near unanimity and repeatedly over time”.12

7 UN Charter. Article 1, paragraph 1. Source: http://www.un.org/aboutun/charter/ 8 Lillich, Richard & Paxman, John. State Responsibility for Injuries to Aliens Occasioned by Terrorist Activities. American University Law Review. Volume 26, 2. 1977. Page 272. 9 General Assembly Resolution 2625, 25th Session, 1970. Source: http://daccessdds.un.org/doc/RESOLUTION/GEN/NR0/348/90/IMG/NR034890.pdf 10 Malzahn, Scott. State Sponsorship and Support of International Terrorism: Customary Norms of State Responsibility. Hastings International and Comparative Law Review. Volume 26. 2002-2003. Page 87 11 Lillich. Supra note 8. Page 271. 12 Malzahn. Supra note 10. Page 87.



At any rate, the Declaration has found more recent confirmation in two other sources of law

that are indeed binding on States: the Security Council and customary international law. As

will be described below in more detail, the former has made clear in several occasions that

harbouring or supporting terrorist groups violates a State’s duties under international law,13

and thus all should refrain from any active or passive assistance to entities or persons

involved in terrorist acts.14 The latter was extensively described by Lillich, who concluded

customary law “expects States to prevent their territory from being used by terrorists for the

preparation or commission of acts of terrorism”.15 In short, every time a non-State actor

perpetrates an armed attack, at least one State did not fulfil its international obligations in the

terms just described.

State sponsorship A second base for analysing attribution of terrorist acts to States is through the work of the

International Law Commission and its Draft Articles on Responsibility of States for

Internationally Wrongful Acts. Chapter Two, which deals with Attribution of Conduct to a

State, identifies only two situations in which terrorist acts committed by private persons may

be attributed to a State: when the perpetration of the attack was controlled or otherwise

directed by such State; and when the conduct of the private actors is a posteriori

acknowledged by the State as its own.

The first is found in Article 8 of the Draft Articles: “The conduct of a person or a group of

persons shall be considered an act of a State under international law if the person or group

of persons is in fact acting on the instructions of, or under the direction or control of, that

State in carrying out the conduct”.16 With regards to the first option – “acting on the

instructions…” –, attribution to a State of conduct explicitly authorized by it is fairly

straightforward, and “widely accepted in international jurisprudence”.17 The second

possibility, determining what degree of direction or control is needed to comply with Article

8, presents more difficulties. 13 UN Security Council Resolutions 748, 1269, 1373 14 UN Security Council Resolution 1373. Source: http://daccessdds.un.org/doc/UNDOC/GEN/N01/557/43/PDF/N0155743.pdf 15 Malzahn. Supra note 10. Page 88. 16 International Law Commission. Draft Articles on Responsibility of States for Internationally Wrongful Acts, with commentaries. Yearbook of the International Law Commission, volume 2, part 2. 2001. 17 Ibid. Commentary 2, page 104.



The problem was tackled by the International Court of Justice in the case Military and

Paramilitary Activities in and against Nicaragua. For many years the case constituted the

established threshold to determine State involvement and, thus, responsibility for the military

actions of non-State actors. The Court was faced with two issues: first, it had to rule on

whether the support provided by Nicaragua to rebels in El Salvador constituted an “armed

attack” by Nicaragua, as to trigger the right to self-defence (exercised collectively, as argued

by the US). Nicaragua had provided weapons and logistical support to rebels intending to

overthrow the government. The Court rejected the US claim to self-defence saying that even

if sending “armed bands” into the territory of another State could constitute such an act of

aggression, the “supply of arms and other support to such bands cannot be equated with

armed attack” against El Salvador.

The second issue was whether the conduct of the Contras, a rebel group operating against the

Nicaraguan government, was attributable to the US so as to hold the latter generally

responsible for their actions. Again the Court held that, even when the US was responsible

for “planning, direction and support” of the Contras, it still found that there was “no clear

evidence of the US having actually exercised such a degree of control in all fields as to justify

treating the Contras as acting on its behalf”.18

Even at the time, the threshold established by the Court was criticized as unnecessarily high,

painstakingly examining each and every Contras action and requesting for hard evidence of

US involvement. The approach was deemed as mistaking the trees for the forest, and

therefore that “States [would] get away with sponsoring terrorists as long as they do not

direct specific acts”.19 Although more recently the Appeals Chamber of the International

Criminal Tribunal for the Former Yugoslavia, in Prosecutor vs. Tadić (not a use of force case

per se), lowered the degree of control necessary to attribute responsibility to that of “overall

control”, rather than specific acts, it still demanded that such level of direction should go

“beyond the mere financing and equipping of forces and involving also participation in the

18 ICJ Summary of Judgment. Military and Paramilitary Activities in and against Nicaragua (Nicaragua vs. United States of America). Source: http://www.icj-cij.org/docket/index.php?sum=367&code=nus&p1=3&p2=3&case=70&k=66&p3=5 19 Malzahn. Supra note 10. Page 101.



planning and supervision of military operations”.20 As it will be seen later on, these

requirements are now being seriously questioned.

The ILC contemplates a second scenario by which the actions of non-State actors may be

attributed to a State. This was codified under Article 11 of the Draft and deals with

situations where actions committed by non-State actors, regardless of prior knowledge,

instruction or control, later become actions attributable to a State “if and to the extent that

the State acknowledges and adopts the conduct in question as its own”.21 The principle

behind the rule was employed by the ICJ in its handling of the case United States Diplomatic

and Consular Staff in Tehran, after thousands of students overran the US Embassy and took

around ninety people hostage – even when the case didn’t involve use of force by the victim

State, its relevance lies in that it discusses the possibility of actions not directed or controlled

by a State be nevertheless attributed to it. Although the Court established that the militants

had initially acted without interference from any public authority, the State of Iran later

became responsible for their actions, first, for refusing to take measures against the militants

and then for publicly approving and perpetuating the hostage crisis for more than a year.

There was little debate on the explicitness of Iran’s approval, as it came from numerous

Iranian authorities, including the Ayatollah Khomeini and other religious, judicial and

executive members of government.

Similarly, the case raised little controversy among scholars.22 However, note should be taken

of the fact that the wording in Article 11 was intended to distinguish cases of

acknowledgement and adoption from cases of mere support or endorsement. As the ILC

explains in its commentary of the Draft Articles, “as a general matter, conduct will not be

attributable to a State under Article 11 where a State merely acknowledges the factual

existence of conduct or expresses its verbal approval of it”.23 As with the Nicaragua case,

recent State practice and opinions would seem to disagree with such interpretation.

20 Case IT-94-1, Prosecutor v. Tadić, ILM volume 38. 1999. Page 1518. As quoted in supra note 16. 21 ILC. Supra note 16. 22 Malzahn. Supra note 10. Page 100. 23 ILC. Supra note 16.



Contemporary thresholds for Stat e re sponsibi l i t y As would seem from the Draft Articles and the ICJ rulings, States ability to find other States

responsible for the actions of non-State actors operating from their territory, and thus trigger

the use of force in self-defence, is severely limited. Even financing, training and providing

logistical support to terrorists, as per Nicaragua, would on paper not be enough. Endorsing or

expressing approval of certain actions wouldn’t make the cut either. The rationale behind

this exceptionally high threshold is twofold: first, it responds to the need to uphold one of

the main purposes of the UN Charter, namely, to restrict use of force as much as possible.

As Cassese explains, “self-defence is an exception to the ban on the threat or use of force

laid down in Art. 2(4) of the UN Charter, which has by now become a peremptory norm of

international law (jus cogens). Like any rule laying down exceptions, that on self-defence must

be strictly construed”.24 Secondly, “a State cannot conceivably be expected to monitor and

prevent all activity within its territory that would violate international norms if committed by

the State itself… States must be able to allocate resources in a manner that balances their

obligations to the international community with obligations to their citizens. No one should

expect poor States, especially, to concentrate their resources solely, or even primarily, on

preventing acts of violence against the citizens or property of other States”.25

Yet the above-described approach to linking non-State actions to States has been severely

criticized as inadequate for the fight against the ‘new terrorism’ of groups like Al Qaeda and

others. The criticism comes from two angles: by comparing it to more recent customary

international law on the subject, and by analysing the all-or-nothing approach to the

interpretation given to the norms.

The former position finds grounds in the argument that both the facts in Nicaragua and the

Iran Hostages cases were different than those facing the international community today: in

neither the territory of a State was used to give assistance or safe harbour to the terrorist

group; both the Contras and the Iranian students were localized threats, not organizations

with worldwide reach; and the ICJ decisions were made in the context of a bi-polar world,

24 Cassese, A. Terrorism is also disrupting some crucial legal categories of international law. European Journal of International Law. Online forum. Source: http://www.ejil.org/forum_WTC/ny-cassese.html 25 Travalio et al. Supra note 3. Page 104.



where armed attacks by proxy agents of either the US or the USSR were fairly common, and

a lower threshold would’ve meant potentially more armed conflicts.26

More importantly, some scholars argue that no matter the ICJ or ILC thresholds, or if it’s at

all possible to equate the facts of past cases with more recent events, current customary

international law has changed substantially in recent years, making previous jurisprudence

obsolete.

Indeed, in the last two decades, States and scholars have consistently attempted to lower the

ICJ and ILC thresholds, arguing that mere support of terrorists by a State should be

sufficient to attribute responsibility for the actions of those terrorists to such State. As was

exposed in Part Two, these attempts have seen a gradual change in the international

community’s reactions, from outright condemnation to muted tolerance to increased

acceptance. In 1993, Schachter commented: “when a Government provides weapons,

technical advice, transportation, aid and encouragement to terrorists on a substantial scale it

is not unreasonable to conclude that the armed attack is imputable to that Government”.27

That same year, the US cruise missile attacks against Iraq for its role in the alleged

assassination attempt against former president Bush received little objection. Five years later,

US attacks against Afghanistan for the bombing of the US embassies in Kenya and Tanzania

received from the international community no reaction at all.28

Similarly, as was mentioned earlier, Security Council and General Assembly’s wording in

their resolutions would also confirm the trend: in 1992, Resolution 748 dealing with the

Lockerbie incident explicitly linked Article 2(4) of the Charter to a State’s legal obligation to

refrain from “organizing, instigating, assisting or participating in terrorist acts in another

State or acquiescing in organized activities within its territory directed towards the

26 Ibid. Page 105. 27 Schachter, Oscar. The Lawful Use of Force by a State Against Terrorists in Another Country, in Henry H. Han, editor, Terrorism & Political Violence: Limits and possibilities of Legal Control. Oceana, 1993.Quoted in Travalio supra note 3. Page 106 28 The bombing of a chemical plant in Sudan as a response for the same attacks was indeed questioned by States at the UN bodies. However, this was due to insufficient evidence produced by the US linking the plant to the production of weapons for Al Qaeda. It was the choice of military target, rather than the legal justification for the actions, that was criticized.



commission of such acts”.29 In 1994, the General Assembly passed the Declaration on

Measures to Eliminate International Terrorism, reaffirming similar responsibilities. The

Council also condemned the notion of “acquiescing” terrorist activities in 1994 and 1998,

and then most certainly in Resolution 1373 of 2001, when the “inherent right of self-

defence” was not only specifically mentioned in the text but directly linked to a set of actions

to be considered “any form of support, active or passive”,30 including suppressing

recruitment of members of terrorist groups, eliminating the supply of weapons to terrorists

and providing safe haven to those who finance or plan terrorist acts. The fact that in 2001

no country raised any objection to the US position that it would “make no distinction

between the terrorists who committed these acts and those who harbour them”, has been

labelled “the strongest manifestation of evolving customary law regarding the use of force

against terrorism”.31

In short, as Beard explains: “while a State may have once argued that the actions of terrorist

organizations did not impose responsibility on that State under Article 2(4) of the UN

Charter and did not subject them to forcible measures in response under Article 51, those

conditions no longer appear to pertain”.32

State support The second criticism to the ICJ and ILC approach to determining State responsibility for the

actions of non-State actors is its intention to reduce it to overly simplified “either-or”

situations. True, both Nicaragua and the more recent developments in State practice, even if

from opposing sides of the argument, attempt to establish a set of conditions to be met, a

threshold which once surpassed, the victim State would be deemed free to take any military

action against another State. As such, just as in 1985 “the US Government’s actions in

supporting the Contras were ultimately treated under the law as being indistinguishable from

countries that had absolutely no connection with the Contras whatsoever”,33 under more

29 UNSCOR 748. Source: http://daccessdds.un.org/doc/RESOLUTION/GEN/NR0/011/07/IMG/NR001107.pdf 30 Idem. 31 Travalio. Supra note 3. Page 109. 32 Beard, Jack. America’s New War on Terror: the case for Self-defence under international law. Harvard Journal of Law and Public Policy. Volume 25. 2001-2002. Page 581. 33 Gibney, M., Tomasevski, K., Vedsted-Hansen, J. Transnational State Responsibility for Violations of Human Rights. Harvard Human Rights Journal. Volume 12. 1999. Page 287.



recent views a State only providing ‘safe haven’, perhaps unwillingly, to non-State actors

would have to accept being equated with a “hostile regime”34 and suffer military operations

in direct violation of its sovereignty.

The matter is not recent and has been tackled by numerous scholars for decades, all in

similar fashion: against the absolutist approach, they propose a scale of State involvement in

the actions of non-State actors operating in their territory, one that allows for the analysis of

more in-between situations.35 Although Brownlie warned that “the sources do not observe

these distinctions and both historically and in recent discussions they have been confused”,36

he thought these varying situations would, in turn, result in distinct questions of

responsibility toward the ‘harbouring’ State, and therefore in a more appropriate set of

responses available against such a State. These degrees of responsibility may or may not

trigger the use of force in self-defence, something that, as will be seen, in some cases it still

remains open to interpretation.

Categorization by scholars is varied: while Malzahn describes three ‘moments’ of

responsibility (State support for a future terrorist attack; breach of the duty to prevent a

current attack; and inability to prosecute or extradite those responsible for a past attack),

Cassese,37 Brownlie38 and Lillich39 divide the continuum into 5 categories, in “a scale of

responsibility beginning with active involvement and descending to benign neglect”.40 The

first of these refers to terrorist actions committed by actual or de facto State agents, be it

public officials or government employees of some other sort. This, of course, is extremely

rare when dealing with non-State actors, as “generally, terrorist groups are not part of the

34 Bush, George W. President Declares “Freedom at War with Fear”. Address to a Joint Session of Congress and the American People. 20th September 2001. Source: http://www.whitehouse.gov/news/releases/2001/09/20010920-8.html 35 Cassese, The International Community’s “legal” Response to Terrorism (infra note 37); Malzahn, State sponsorship and support for International Terrorism (supra note 10); Lillich, State Responsibility for Injuries to Aliens… (supra note 8); Brownlie, International Law and the Activities of Armed Bands (infra note 36). 36 Brownlie, I. International Law and the Activities of Armed Bands. International and Comparative Law Quarterly. Volume 7. October 1958. Page 713. 37 Cassese, A. The International Community’s “Legal” Response to Terrorism. International and Comparative Law Quarterly. Volume 38. July 1989. 38 Brownlie. Supra note 36. 39 Lillich. Supra note 8. 40 Ibid. Page 308.



official apparatus of any State”.41 Examples, however, include the 1986 Berlin bomb in a

discotheque, effectively attributed to Libyan agents acting for the State of Libya; the attack

on Greenpeace’s Rainbow Warrior, carried out by French secret service agents; and the

assassination of Abu Jihad, a prominent PLO leader, by Israeli security forces.42

The second option includes situations whereby a State employs unofficial agents to conduct

its operation, rather than its own officials. These agents could be simply mercenaries or

organized armed bands, but their actions are effectively commanded by the State, who plans

and has the final word on all decision-making. As with the first setting, in this case

“international law is clear: the terrorist attack is attributable to the State and a use of force

against it by way of individual or collective self-defence is allowed”.43 Debate on these cases

is minimal, as the cases comply with both the ILC and ICJ thresholds, the 1970 Declaration

and UN Resolutions. In short, “traditional norms fit like a glove”.44

From here on, establishing the link between the State and the terrorist action is less

straightforward. The third category of State involvement deals with situations where the

non-State actor acts independently of State authority, has final discretionary power over its

actions, yet receives weapons, logistical support and/or funds from a State. Nicaragua dealt

with such a scenario, with the results already described: while the Court considered the case

insufficient to attribute responsibility, Judges Schwebel and Jennings45 and other scholars46

emphatically disagreed. Considering more recent developments in State practice and the

controversy it generated at the time, it would be safe to say that, currently, this level of active

State participation in the operations of terrorist groups may be considered enough grounds

to attribute a terrorist armed attack to the State, and thus trigger the use of force in self-

defence against such State – even when there are still those who would reject this.

41 Cassese. Supra note 37. Page 597 42 More information on: The Assassination of Abu Jihad. Journal of Palestine Studies, Vol. 17, No. 4. Summer, 1988. 43 Cassese. Supra note 37. Page 598. 44 Lillich. Supra note 8. Page 308. 45 ICJ Ruling. Supra note 18. Parags. 346 and 543. 46 Lillich, Cassese are examples.



So far, State involvement has been decided upon its active role in the work of non-State

groups. Situations may arise, however, in which the State does not provide any resources to

an organization, yet still allows it to operate freely within its territory. In this scenario,

liability is established upon the State’s “failure to use ‘due diligence’ to prevent [a terrorist

act’s] occurrence. For sure, a State cannot be expected to prevent every act of international

terrorism occurring or originating within its borders. If so, West Germany would also have

been found at least partially responsible for the Berlin bombs and September 11th.47 What

would be expected is that States take all necessary measures, within reason, to protect the

rights of other States. Of course what actions would be deemed necessary or reasonable can

only be determined in a case-by-case basis, by studying the measures taken, resources

employed, historical background information, inter-State relations and other factors. The ICJ

provided some light on the concept of due diligence in the Hostages case, when it explained

that it is breached when a State is “aware of the need for action on [its] part… but fails to

use the means which were at [its] disposal”.48

This two-tiered test of due diligence, being aware of the need for action and the failure to

take the measures at its disposal was also employed by the ICJ during the Corfu Channel case.

After two British warships sustained important damage due to mines located in Albanian

territorial waters, the Court concluded that Albania could not have been unaware of the

existence of such threat, as they could not have been laid “without the knowledge of the

Albanian Government”.49 Following such assertion, Albania was found to have breached its

duty to warn Britain of the mines, a “conduct which was most easily within the power of the

Albanian Government”.50

The sporadic nature of terrorist “armed attacks”, a characteristic briefly mentioned above,

means the due-diligence test must be applied both before and after an attack is perpetrated.

As such, under customary international law not only must a State attempt to prevent the

47 See note 5 for information on the Hamburg Cell. 48 ICJ Summary of Judgment. United States Diplomatic and Consular Staff in Tehran. Source: http://www.icj-cij.org/docket/files/64/6291.pdf 49 ICJ Summary of Judgment. Corfu Channel. Source: http://www.icj-cij.org/docket/files/1/1647.pdf 50 Malzahn. Supra note 10. Page 104.



commission of a crime it is aware of, but also to seek, capture and prosecute or extradite the

non-State guilty parties in good faith.51

With regards to the possibility of victim States using force against a State in breach of its

duty to prevent or punish non-State actors’ actions, the case remains unsettled. Although

Cassese would argue against it (see above), as did the ICJ in Nicaragua, others like Dinstein

believe this “passive assistance” or acquiescence does give rise to a right to military self-

defence.52 Less assertively, Brownlie suggests the case has been put forward in several

occasions during the 20th century, even before the UN Charter: in 1916, Lansing, US

Secretary of State, argued for the legality of a US force sent into Mexican territory to

disperse rebels due to the unwillingness of Mexico to remove the menace; in 1921, Soviet

troops entering Mongolia were also justified after the failure, in spite of repeated requests, of

the Chinese Government to deal with White Guard bands. In all cases, the use of military

force in and against the passive State was accepted as legal.53

The last scenario possible is one in which non-State actors perpetrate an armed attack

without any assistance, active or passive, from the State in which they operate.54 The

possibility has been carefully ignored by some scholars (and States), or treated jointly with

the previous category; that is, if a terrorist group is found to operate from certain State’s

territory, such State is automatically found liable for the group’s actions. Yet a State unable

to take action, or whose measures taken in good faith prove insufficient to prevent an attack,

should not bear the same responsibility as a State that is clearly unwilling to prevent or

punish non-State actions. Two factors must be taken into account:

First, the question of sovereignty. As has been discussed earlier, the general norm codified

under Article 2(4) is that all States should refrain from using force against the territorial

integrity and political independence of another State. As such, if an armed attack perpetrated

by a terrorist group cannot be seen to be caused by specific actions (active support) or the

51 Oppenheim, L. International Law. Cited in Malzahn, supra note 10. Page 105. 52 Dinstein, Yoram. War, Aggression and Self-defence. Cambridge University Press. Fourth Edition. 2005. Page 206. 53 Brownlie. Supra note 36. Page 733. 54 Although some have considered this possibility by imagining an attack originating from bases in the high seas or outer space, such a situation not only is highly unlikely, but there would be little debate around the victim State using force in self-defence against the non-State camps.



lack of due diligence (acquiescence) attributable to the State from where the attack

originated, then the general prohibition upon which the international community based its

relations in 1945 should, in principle, prevail. As is commonly reminded when describing the

terrorist threat, the resources available to some organizations are seemingly endless; in

contrast, the State fighting their presence could be a failed State, economically outperformed

by the non-State actor55 or plain inefficient. In such situations victim States must find

themselves bound by the hierarchy between the two types of responses to terrorism,

peaceful over coercive, as laid down in the UN Charter and subsequent basic texts.

Surely this view is by no means universal, particularly in light of the new ‘catastrophic

terrorism’.56 But as most scholars would agree that under both customary international law

and the UN Charter military force is to be used only when absolutely necessary,57 it should

follow, as Cassese explains, that “only after every effort has been made to deal with a

terrorist attack by peaceful means should States resort to military action”.58 In this scenario,

the difference between a State that is not unwilling, but rather just unable to prevent an

armed attack originating from its territory is vital. Exposing the situation could result in

effective collaboration between the victim and harbour States, foreign assistance, or at least

in the express authorization (i.e. consent) from the struggling Government for another State

to enter its sovereign territory (and of course the State would have to agree to these

measures to remain in the clear). Travalio believes “a State cannot use force against a State

providing sanctuary or support to terrorist groups unless that State has been given the

opportunity to remove the terrorist from its soil or cease its support”. States willing but

unable to do so should be provided with at least the same treatment, if not a better one.

Summary As has been discussed along this section, even after the occurrence of an armed attack is

established, a State’s military response in self-defence, though lawful, will still be limited by

the fact that, between aggressor and victim, lie the territorial integrity and political

55 According to some reports, Al Qaeda was the de facto authority in at least large portions of Afghanistan, with the Taliban far from ‘allowing’ their presence but rather completely subjected to it. 56 Annan, Kofi. In Larger Freedom. Report of the Secretary General to the General Assembly, 59th Session. 21st March 2005. Paragraphs 87-96. Source: http://daccessdds.un.org/doc/UNDOC/GEN/N05/270/78/PDF/N0527078.pdf 57 Travalio et al. Supra note 3. Page 113. 58 Cassese, supra note 37. Page 591.



independence of another State. Over the last decades, continuous attempts have been made

to determine the level of responsibility this ‘third party’ holds for the actions of private

individuals, mainly to decide if a victim State could use force against it or against the terrorist

organizations working from it. Though far from universally accepted, there is clear evidence

that the general trend in State practice is a move toward a relaxation of the ICJ and ILC’s

thresholds. How low will the threshold remain is still undetermined (and may have to wait

for judicial bodies as the ICJ to rule on new sets of facts). Yet as much as global terrorism is

an ever-increasing threat to all, care should be exercised by States victim of attacks to

determine the level of responsibility attributable to other States, as to restrict the exercise of

their right to self-defence to situations of last resort – as was envisioned by the drafters of

the UN Charter – and only against those willingly positioned on “the wrong side of the war

on terrorism”.59

59 Statement by Ambassador John Negroponte, United States Permanent Representative to the United Nations. 5th October 2003. Source: United States Mission to the UN, http://www.un.int/usa/03_153.htm



Part Four. Responding or preventing? Necessity and proportionality in the use of force against non-State actors

After dealing with the concept of armed attack by non-State actors, Part Three discussed the

possibility of attributing responsibility to a State for the actions of private groups. The issue

is of crucial importance insofar as the use of force in self-defence almost inevitably results in

the trampling of some State’s sovereignty. While the ICJ and ILC have established

particularly high thresholds, State practice and scholarly writings have continuously pushed

for more leeway. Although 9/11 definitely provided with grounds for such position, more

recent Security Council resolutions would seem to show that the initial enthusiasm has now

rescinded.1

Of course, use of military force can be legally justified. If a State is victim of an armed attack,

Article 51 enters into play automatically.2 If evidence gathered suggest a State actively

supported or did not fulfil its duty to exercise due diligence with regards to the attackers,

then it may be found responsible and forced to accept the consequences of having the victim

State conduct military operations within its sovereign borders.

Resort to force in self-defence, however, is not unrestricted. Much to the contrary, it is

absolutely dependent on considerations of necessity and proportionality, principles which if

not met, would render any action taken in self-defence unlawful. The following section will

discuss these as applied to military operations carried out against non-State actors, from

three angles: that of the action, the perpetrator, and the military targets against which a State

may aim its response.

Necess it y agains t non-State ac tors As was described in Part One, the notions of necessity and proportionality as applied to self-

defence have one main objective: to constrain the use of force as much as possible, in

1 Gray, Christine. International Law and the Use of force. Oxford University Press. 2004. Page 187 2 Even when the discussion on State responsibility could be read as an attempt to limit this resort to force, the fact remains that once a State is victim of an armed attack, self-defence becomes a legal option. Details as to the where and the when of the military response are considerations a posteriori.



accordance with the purposes stated in the UN Charter.3 The principles apply to all stages of

the self-defence paradigm: first, they demand force be resorted to only if a peaceful solution

to the conflict is impossible to achieve.4 Secondly, they limit the force used to that which is

necessary to confront the enemy threat. Forcible actions beyond this need are considered

punitive action or reprisals, and thus generally impermissible.5 Thirdly, they pose limitations

as to the choice of targets the victim State may aim to destroy.

Once a peaceful solution is considered unreachable, States focus on what does it entail to

deal with the enemy threat. Unfortunately, this issue remains unclear. Traditionally, scholars

have directed their attention to that which triggers self-defence in the first place, i.e. the

‘armed attack’ itself: Gray, for example, defines necessary force as that which “halts and

repels an attack”.6 Greenwood agrees: “The requirement of necessity in self-defence means

that it is not sufficient that force is used after an armed attack, it must be necessary to repel

that attack. The use of force in response to an armed attack that is over and done with does

not meet that requirement and looks more like a reprisal” (emphasis added).7

This focus on the action triggering self-defence poses several problems to the lawful use of

force against non-State actors. These were analysed by Paust when dealing with the Berlin

discotheque bomb and the US military reaction against Libya, carried out some ten days after

the events in Germany: “the lull of ten days presents the problem of whether or not there

was force actually used to repel an armed ‘attack’. What attack, one might ask?”8 Given the

modus operandi of terrorist groups, the same question could be asked of any response to a

terrorist act: Operation Enduring Freedom was launched under the auspices of the international

community, most particularly Security Council Resolution 1373 and its explicit reference to

self-defence; yet the response was executed a month after the attacks on the World Trade

3 Cassese, A. Terrorism is also disrupting some crucial legal categories of international law. European Journal of International Law. Online forum. Source: http://www.ejil.org/forum_WTC/ny-cassese.html 4 Ago, Roberto. Addendum. Eight report on State responsibility by Mr. Roberto Ago, Special Rapporteur – the internationally wrongful act of the State, source of international responsibility (part 1). Extract from the Yearbook of the International Law Commission. Volume II. 1980. Page 69. 5 Paust, J. Responding Lawfully to International Terrorism: the Use of force abroad. Whittier Law Review. Volume 8. 1986-1987. Page 730. 6 Gray, supra note 1. Page 123. 7 Greenwood, C. International Law and the Pre-emptive use of force: Afghanistan, Al-Qaida, and Iraq. San Diego International Law Journal. Volume 4: 7, 2003. Page 23. 8 Paust. Supra note 3. Page 730



Centre were over. Following Paust’s logic, how did the US response in Afghanistan help

repel such armed attack? “The US action has therefore been criticized for constituting what

some consider to have been a reprisal, rather than a genuine action in self-defence”.9

Attempting to provide viable solutions to these concerns, some scholars have suggested

alternative options: the first of these refers to a reinterpretation of the notion of armed

attack by a non-State actor. Traditionally, terrorist attacks have been considered sporadic,

non-continuous, distant in time and place and originating from an irregular, constantly

metamorphosing source. Yet it is also true that none of the attacks perpetrated by a group

like Al Qaeda occurred or should be considered in isolation.10 As such, should 9/11 be put

together with such others as the attacks on the US embassies in East Africa, the USS Cole,

and more recently Madrid, East Asia and London, the application of the “regular” concept

of necessity would be greatly facilitated: by constituting a continuous, multi-faceted attack,

spread over time and places, but still in motion, military action by the victim States would

respond not to a single event that is already ‘over and done with’, but as repelling an ongoing

armed attack. In practical terms, limiting the laws of self-defence to pairs of “one event-one

State response” makes it impossible for any State to comply with the ‘necessity’ factor, as it

would always lag a step behind trying to catch the perpetrators “in the act”. Expanding the

duration of such act, albeit in a somewhat sui generis fashion, provides a better fit for the

norms of self-defence and its principles.

A second approach refers to the concept of necessity focusing on the perpetrator of the

attack, rather than on the attack itself. Printer proposed this view in his analysis of a US

attack against Al Qaeda members in Yemen: “Whether the attack […] was warranted

depends on whether there existed a continued military necessity, as required by the jus ad

bellum, which justified the right to self-defence. Recall that necessity is not a temporal limit

on the right to use counter force. The defending party may use responsive force until the

enemy is defeated.” Two elements call for attention in such explanation: first, the direct

contradiction with previous readings of the concept of necessity concerning the timing of

the response. As described above, the notion of taking actions necessary to repel an attack

9 Greenwood. Supra note 6. Page 23. 10 Greenwood. Supra note 6. Page 23.



implicitly poses a time limit to such actions,11 given that if such actions serve no longer a

purpose strictly related to the armed attack, then it is too late to act.

Secondly, he focuses on the force necessary to defeat the enemy, not to repel a mere attack,

clearly placing higher importance on the non-State actor as a permanent threat rather than on

the attack itself. In inter-State relations, an armed attack would not be seen as grounds for

the absolute elimination of the aggressor; in fact, its existence after the armed conflict would

not be put in doubt. This concurs with the principle of proportionality: a State acting in self-

defence must limit its response so that the harm inflicted upon the aggressor is not excessive

compared to that suffered by the initial attack. As such, only should the very survival of the

State be at stake could the absolute destruction of the attacker be justified.12 Yet it is hard to

conceive States reaching to an agreement and establishing any sort of diplomatic relations

with an organization whose main raison d’être is to perpetrate armed attacks against them, and

nothing else. Therefore, should a State limit itself to repel attacks time and time again, or

should the very concept of necessity impel it to eliminate the threat to its existence in its

entirety? The current US position would seem to point in this direction.

The neces s it y to deal wi th fu ture at tacks : Ant ic ipatory s e l f -de fence The above-described options both refer to restraining use of force to that necessary to deal

with past events. A third alternative suggests States respond by taking measures necessary

not to repel (as Gray demands) but rather to anticipate a future attack. The concept has been

almost universally accepted as a lawful approach to self-defence.13 It allows for the use of

force on one condition: that the occurrence of an armed attack is imminent.

Applied to non-State actors, the argument is simple: clearly, groups such as Al Qaeda intent

to perpetrate further attacks. Past actions, together with explicit public statements14 provide

the “clearest possible indications of further outrages to come”.15 In these circumstances, the

11 Some scholars consider the concept of immediacy the third principle of a lawful use of force in self-defence. It has been this paper’s position to treat the factor of timing as inherent to the concept of necessity and not as an independent concept. 12 ICJ Advisory Opinion: Legality of the Use or Threat of Nuclear Weapons. Source: http://www.icj-cij.org/docket/index.php?p1=3&p2=4&k=e1&case=95&code=unan&p3=5 13 See Part One, Section The Concept of Armed Attack. Page 16 14 New York Times, 11th September 2003. Page A1. 15 Greenwood. Supra note 5. Page 23.



requisite of meeting the criteria of imminence could be considered fulfilled, a position that

has found little objection from scholars.16 Added to the fact that anticipatory action complies

with the requirement of an armed attack – even if such attack is only on the verge of

materializing, legitimacy is found in that the response complies with the terms of both

Article 51 of the UN Charter and customary international law.17 This was Greenwood’s

conclusion to his analysis of US military action taken post-9/11: “as long as military action in

Afghanistan is viewed as a forward looking measure to prevent an imminent threat from

materializing into violence, rather than as a backward looking act of retaliation for the events

of 9/11, this criterion of self-defence appears to be satisfied”.18

Choi ce o f targe t s and the princ iple o f proport ional i t y Be it in response to an armed attack or as anticipation against future non-State actions, the

principles of necessity and proportionality continue to restrict States’ choices once military

action in self-defence is set into motion. The theory is much less contested: a State may only

choose to target those military objectives19 whose destruction is deemed as necessary to deal

with the threat, and its use of force must remain proportionate “not to the massacre caused

by the terrorists […] but to the purpose of such use, which is to detain the persons allegedly

responsible for the crimes and to destroy military objectives, such as infrastructures, training

bases and similar facilities used by the terrorists”.20

As for the ‘host’ State’s troops and military facilities, their eligibility as targets should remain

subject to the State’s level of responsibility in the activities of the non-State actors (discussed

in Part Three). Again, the principle of necessity provides a guideline: a State offering active

support of a terrorist group will probably support it militarily once hostilities begin, making

it necessary for the victim State to act against the ‘host’ State forces as well. A State willing

but unable to eliminate terrorist groups within its territory would not limit the victim State’s

response in any way, making it unnecessary for it to be targeted. State practice,

16 Greenwood. Supra note 5. 17 Jurisprudence can be traced back to the Caroline case: the UK acted in anticipation to an imminent armed attack by rebel groups acting from the US. Its actions were deemed lawful given that they proved to show “a necessity of self-defence, instant, overwhelming, leaving no choice of means and no moment for deliberation”. (Webster, Part One, supra note 34). 18 Greenwood. Supra note 5. Page 23. 19 All resort to force is bound by the principles of humanitarian law. 20 Cassese, supra note 3. Page 7.



unfortunately, has been much less transparent, and consequently subject to intense criticism

and scholarly debate.21

Summary As with most of the self-defence paradigm, the parameters of necessity and proportionality

pose difficulties when attempted to be applied to the actions perpetrated by non-State actors.

Though through different interpretations, there is general consensus, however, in that these

parameters must continue to restrain State’s use of force as much as possible, in line with the

general purposes of the United Nations and its Charter.

21 For an analysis of the US response in Libya, see Paust, supra note 3. US response in Yemen, see Printer, Jr., Norman. The Use of force against non-state actors under International Law: An Analysis of the US Predator Strike in Yemen. UCLA Journal of International Law & Foreign Affairs. 2003.



Conclusions As has been pointed out a number of times, one of the international community’s main

objectives in 1945 was to restrict the use of military force as much as possible. This was the

general will of nations at the time, all of which agreed not only to the explicit language in

Article 2(4) of the UN Charter, but also to the numerous limitations entailed in the lawful

exercise of the right to self-defence: the requisite of the occurrence of an armed attack as

only triggering factor, the appropriate attribution of responsibility for such armed attack, and

the compulsory adherence to the notions of necessity and proportionality.

The rules were designed by States and aimed to deal with belligerent States. The irruption of

non-State actors with transnational operational capabilities and violent methods has forced

the situation to be carefully re-appraised. Can non-States perpetrate attacks in the terms

established in the rules of States? If so, who in the international scene is to blame for their

actions? Should States be bound by their own rules if responding to non-States? As has been

extensively discussed throughout this paper, there are no definitive answers to any of these

questions. The general trend, however, would seem to point in the following direction:

This non-State actors, though newcomers to the scene, have proved themselves capable of

perpetrating attacks on the same scale as States, if not more horrendous due to their

indiscriminate nature. Though traditionally the community of nations did not consider them

“armed attacks” in the terms of Article 51, practice gradually changed en route to 9/11, when

it turned over completely. How far will this change go in scope and time, it is still impossible

to tell. As for responsibility for the actions of private actors, again the situation seems to be

in rapid change. Yet scholars’ push for lower thresholds than those established by the ICJ

and the ILC should be taken with care: as long as the use of force remains a measure of last

resort, extreme restraint should be taken in the attribution of responsibility to States for the

crimes of private organizations. Finally, if force is indeed the only option available, States

should still limit their military options to those absolutely necessary to respond to the threat,

and nothing more.



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