The Case for Pre-emption (Not Prevention) in Public International Law

by Jeff Collins

In part due to the American invasion of Iraq in 2003 and in part due to the diversity of external threats that states now face in a post-Cold War era, much discussion has arisen in the past decade on when states may, unilaterally, use force to defend themselves outside of the restrictive parameters of the United Nations Charter. The two arguments advanced by a number of states and commentators that would permit a state to unilaterally use force in self-defence are pre-emption and prevention. Unfortunately, over the preceding decade both terms have been used interchangeably (as exemplified in the 2002 US National Security Strategy) to such an extent that confusion now exists over whether there is any real distinction between the two. In actuality, although both terms fall under the category of anticipatory self-defence they are distinct arguments separated, at their crux, by a “matter of timing.”[1] In short, pre-emption is to be initiated on the premise that an external attack is imminent while prevention is initiated on the belief that an armed attack is likely to occur in the future and “that delay would involve great risk”.[2]

This paper will argue that only one of these arguments, pre-emptive self-defence, can be justified in public international law (henceforth, international law), while the other cannot. Therefore, this paper will elaborate on the distinctions between these two forms of anticipatory self-defence and explain why there exists a claim for pre-emption in international law but not prevention. However, in order to best appreciate the argument brought forth, this paper will provide a brief overview of the use of force in international law.

International law can be divided into two types: customary international law and treaty law. The principles derived from customary international law come from state practice (what the majority of states do) and opinio juris (what states say). Customary international law is seen as running parallel to treaty law unless an international treaty includes a(n) article(s) that strictly discounts a principle of customary international law. In that case, the law of the treaty takes primacy between the parties to the treaty. The most prominent treaty in the world today is the United Nations Charter (henceforth ‘Charter’) of which the world’s states are members. Written in the aftermath of the Second World War in 1945 the principle aim of the Charter is “to save succeeding generations from the scourge of war […]”.[3]

Of the 111 articles that make up the Charter the most relevant to the use of force (jus ad bellum) are those found in Chapter VII and Article 2(4). The Charter, given its aim, prohibits the use of force in international relations. Article 2(4) encapsulates this: “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”.[4] However, there are two exceptions to this rule: self-defence and force authorised by the Security Council.

Self-defence is articulated in Article 51: “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 […]”.[5]The other exception relies on the Security Council’s Chapter VII powers to determine whether or not a state (or non-state actor; see Resolution 1368) constitutes a threat to international peace and security. For the purposes of this paper, however, the focus will be on Article 51. By emphasising that self-defence can only be used in the event of an armed attack this Article is seen by some commentators as being read too much in a restrictive manner for it not only disavows the use of force pre-emptively but prohibits the whole concept of anticipatory self-defence as a violation of Article 2(4).[6] For other commentators, like international lawyer Michael Wood, Article 51 should be viewed as a derivative of the customary international law principle of an ‘inherent right [to] self-defence’. Given that this principle is incorporated into the Charter, it is therefore possible for a state to use of force pre-emptively as this form of self-defence was accepted in pre-Charter customary law.[7] It is on this point that this paper will make the argument for the existence of a legal basis for pre-emptive self-defence.

As Taft notes, the purpose of the UN Charter’s language in preserving the inherent right of self-defence is to help dissuade states from taking aggressive action.[8] That may have been fine in 1945 but if the Charter is to be relevant in today’s threat environment it must take into account the destructiveness and technical features of modern weapon systems.[9] A restrictive reading of the Charter actually relegates the document to the Cold War era and not to the drastically changed times we live. To elaborate, in 1945 there was one nuclear power, today there are at least nine, of whom four are not members of the Non-Proliferation Treaty regime and are thereby not privy to international inspection. Two of these four members of the nuclear club are of great concern to global stability. The first, Pakistan, faces much internal instability and has had members of its nuclear program (chiefly A.Q. Khan) provide nuclear know-how on the black market, thereby contributing to further horizontal proliferation to potential hostile states.[10] The second, North Korea, is a nation with a strong history of aggressive behaviour towards its neighbours (e.g. the unprovoked sinking of a South Korean warship in March 2010 and artillery barrage in November 2010) and of providing proliferation services to Iran (in the form of long range missiles and nuclear technical expertise) and Burma.[11]  In such a world, states need to be able to defend themselves appropriately; for example, a restrictive reading of the Charter would not help Japan if it determined that North Korea was going to fire a nuclear armed missile at it.

Fortunately, voices within the UN are also drawing the same conclusions. In the aftermath of the invasion of Iraq, a UN High Level Panel on “Threats, Challenges, and Change” convened in 2004 to discuss threats currently facing states and how the UN Charter measures up to these threats. While acknowledging that the Charter is perfectly fine to restrict the use of force it did mention that in international law, “a threatened State, according to long established international law, can take military action as long as the threatened attack is imminent, no other means would deflect it and the action is proportionate”.[12] The long established law the Panel was referring to is found in customary international law and dates from a case in 1837, known today as the Caroline incident. The Caroline was a privately-owned American ship alleged to have been supporting Canadian rebels in their fight against the British Crown when, in 1837, British forces crossed the international border, seized the ship, killed one of its crew and then scuttled it. In an exchange of letters between the two protagonists, Britain declared that it was acting in pre-emptive self-defence as the ship was known to be supplying rebels from US territory and the Americans were doing nothing to stop it. In what now remarks as an influential statement, then US Secretary of State, Daniel Webster, replied in a letter to his British counterpart that for “force to be used in self-defence it will be for the government to show a necessity of self-defence, instant  [and] overwhelming, leaving no choice of means, and no moment for deliberation”.[13] This statement has been refined to what is now known as the Caroline criteria for pre-emptive self-defence: the use of force must be necessary, proportionate, and in the face of an immediate threat.[14]

Over the years, this criteria and its associated claim for pre-emptive self-defence have never been repealed or discounted in either treaty law or by the opinions of the Security Council.[15] For instance, both the Kellogg Briand Pact of 1928 and the League of Nations never excluded pre-emptive self-defence.[16] The Caroline criteria were also used during the Nuremberg tribunals in the face of Germany’s claims that its invasion of Norway in 1940 was an act of pre-emptive self-defence. Notably, the tribunal acknowledged the existence of the criteria but rejected Germany’s invocation of it – given the undisputed facts of Germany’s aggression.[17] Unfortunately, the bi-polar nuclear tensions during the Cold War kept “discussions on pre-emptive force minimal”.[18]

Nevertheless, as UK international lawyer Christopher Greenwood states, “[the] practice since 1945 tends to support that conclusion and confirms that the right of self-defence in the Charter era continues to include a right to use force to avert imminent armed attack”.[19] This is also echoed by legal scholar Yoram Dinstein, who wrote that, “the imminence of an armed attack does indeed justify an early response by way of interceptive self-defence”.[20]  There are a number of examples over the past six decades that tend to reinforce this argument. For instance, Helinke states that during the Cuban Missile Crisis in 1962 the US could have acted pre-emptively if it wanted to.[21] Greenwood points out that the Six Day War is a classic case of pre-emptive self-defence even though, for political reasons, Israel opted to publicly defend itself on the grounds of Article 51.[22] As the esteemed international lawyer Thomas Franck noted, the Six Day War “does recognise that, in demonstrable circumstances of extreme necessity, anticipatory self-defence may be a legitimate exercise of a State’s right to ensure its survival”.[23] When the issue of pre-emptive self-defence came before the Security Council in 1981, this time concerning Israel’s attack on the Osirik reactor in Iraq, the Council not only implicitly recognised a claim of pre-emptive self-defence but in fact criticised Israel for not meeting the Caroline criteria.[24]

Nevertheless, the presence of a right of pre-emptive self-defence is not a carte blanche excuse for states to use force whenever they feel threatened. The Caroline criteria are quite explicit on when such a right can be invoked. As Dinstein wrote, “the contention that mere mobilization or ‘bellicose utterances’ as such may justify self-defence within the framework of Art. 51 has no foundation”.[25] The threshold to imminence is quite high and the right to pre-emptive self-defence can only be invoked “in response to an armed attack as soon as it becomes evident to the victim State (on the basis of hard intelligence available at the time) that the attack is in the process of being mounted”. [26] The two Israeli incidents mentioned above would seem to confirm that state practice acknowledges pre-emptive self-defence to be restricted to those “instances where the armed attack is imminent”.[27] With the claim to pre-emptive self-defence now stated, we now turn to briefly examine the concept of prevention in international law.

The main problem that preventive self-defence poses to international law is that it is based on the “differentiation between potential and reality, between intention and action”.[28] To experts of international relations, preventive war appears to be nothing more than a “war of choice that derive[s] mostly from a calculus of power, rather than the precedent of international law, conventions, and practices”.[29] Others have noted that preventive self-defence is a “prescription for adventurism and global instability” that can set dangerous precedents should it be practiced more often.[30] There are also some practical legal aspects to a preventive war doctrine given that nowhere in either Charter or customary international law has there existed such a claim.[31] Christine Gray identifies other practical legal problems with preventive self-defence, as she posits that its proponents cannot provide clear answers to such questions as ‘what will trigger action? What form of preventive action will take place? What is the role of the United Nations?’[32] Another practical issue with preventive war, though not quite a legal one, is the role of intelligence. Technically, in preventive wars intelligence is given a “more circumscribed role”.[33] As such, the decision to “wage preventive war rests on an assessment of likely future conflict with a state, based on an assessment of trends and risks rather than immediate intentions, capabilities and plans”.[34] The risk coming from this process is that decision makers may be inclined to “use intelligence to make the future appear more certain than it could be, thus steering [their] country towards a more belligerent policy”.[35]

Lastly, the claim for preventive war, as articulated in the US 2002 National Security Strategy and frequently invoked in the run-up to the 2003 invasion of Iraq, appears to have few adherents. Given that preventive self-defence was invoked as a reason to invade Iraq it is notable that the majority of the world’s states were in opposition to the war; this would tend to suggest that the international community does not accept an inherent claim to preventive self-defence.[36] As state opinion and practice is required to contribute to the development of international law then clearly, as of today, there are no legal grounds for preventive war other than an appeal to the Security Council. Also of relevance, of the 45 states that did offer US military or political support “none did so on the basis of the doctrine of preventive self-defence”.[37]

In conclusion, this paper has made the argument that there does in fact exist in international law a claim for pre-emptive self-defence. As stated earlier, the current nature of the international system since the end of the Cold War seems to have “changed the calculus of action and the desirability of pre-emption”.[38] Today, the threats of weapons of mass destruction proliferation, failing states, and mass casualty terrorism have increased threat levels to the point where pre-emptive action against such threats is “the most efficient way to deal with the issue of securing a state’s safety given the absence of an effective collective security mechanism”.[39] That being said, there does not exist a claim for preventive self-defence in international law. However, should such a right be invoked it would pose serious practical problems to the functioning of international law in addressing conflict and, as such, should be avoided.

[1] Council on Foreign Relations, ‘The Bush Administration’s Doctrine of Preemption (and Prevention): When, How, Where?’, CFR,February 1, 2004, Accessed November 29, 2010, Available at

[2] Bobbitt, P., Terror and Consent: The Wars for the Twenty-First Century, Penguin Books, 2008, p. 136

[3] United Nations, ‘Charter of the United Nations’, United Nations, 1945, Accessed December 15, 2010, Available at

[4] Ibid.,

[5] Wood, M., ‘The Law on the Use of Force: Current Challenges’, Singapore Year Book of International Law, Volume 11, Number 1, 2007, p. 6

[6] Soafer, A.D., ‘On the Necessity of Pre-emption’, European Journal of International Law, Volume 14, Number 2, 2003, p. 212

[7] Wood, p. 6

[8] Taft, W. H., IV, ‘The Legal Basis for Preemption’, Council on Foreign Relations, November 18, 2002, Accessed November 29, 2010, Available at

[9] Ibid.,

[10] BBC News Online, ‘Profile: Abdul Qadeer Khan’, BBC News, February 20, 2004, Accessed December 14, 2010, Available at

[11] BBC News Online, ‘Wikileaks: North Korea ‘helps Burma with nuclear sites’, BBC News, December 9, 2010, Accessed December 10, 2010, Available at

[12] United Nations,  A more secure world: Our shared responsibility: Report of the Secretary-General’s High-level Panel on Threats, Challenges and Change, December 2, 2004, Accessed December 14, 2010, Available at, para 188, p. 54

[13] Helinke, B., Under Attack: Challenges to the Rules Governing The International Use of Force, Ashgate Publishing Ltd., 2010, p. 151

[14] Ibid., p. 151

[15] Bjola, C., Legitimising the Use of Force in International Politics: Kosovo, Iraq, and the Ethics of Intervention, Routledge, 2009, p. 136

[16] Helinke, p. 151

[17] Ibid., p. 151

[18] Ibid., p. 152

[19] Greenwood, C., Essays on War in International Law, Cameron May, 2007, p. 173

[20] Dinstein, Y., War, Aggression and Self-defence, Cambridge University Press, 2005, p. 182

[21] Helinke, p. 152

[22] Greenwood, p. 674

[23] Ibid., p. 674

[24] Ibid., p. 674

[25] Dinstein,p. 186

[26] Ibid., p. 186

[27] Greenwood, p. 676

[28] Helinke, p. 149

[29] Council for Foreign Relations, ‘The Bush Administration’s Doctrine of Preemption (and Prevention): When, How, Where?’,

[30] Lasenksy, S.C., ‘Right War, Wrong Doctrine,’ Council for Foreign Relations, March 30, 2003, Accessed November 29, 2010, Available at

[31] Dinstein, p. 185

[32] Gray, C., International Law and the Use of Force, Oxford University Press, 2004, p. 183

[33] Council on Foreign Relations, ‘The Bush Administration’s Doctrine of Preemption (and Prevention): When, How, Where?’,

[34] Ibid.,

[35] Ibid.,

[36] Gray, p. 177

[37] Ibid., p. 183

[38] Council on Foreign Relations, ‘The Bush Administration’s Doctrine of Preemption (and Prevention): When, How, Where?’,

[39] Helinke, p. 149

Jeff Collins’ Bio: Jeff holds both a BA in Political Science and History and a Certificate in Public Administration from Memorial University of Newfoundland, Canada; a Law degree from the University of Aberdeen, UK; and a MA in International Relations and Strategic Studies from the University of Birmingham, UK. His research interests include international security, Canadian defence policy, Israeli security issues, and international law. At the moment he is examining the use and implications of armed drones in warfare. He currently resides in Fredericton, Canada and can be accessed on twitter at!/JeffCollins6


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