Ethics & International Affairs Volume 17.1 (Spring 2003): Roundtable: Evaluating the Preemptive Use of Force: Letting the Exception Prove the Rule [Full Text]

Mar 2, 2003

It is unlikely that George W. Bush feels constrained by international law when deciding whether to use military force abroad. Nevertheless, many of the United States’ allies are reluctant to cooperate with and participate in military actions that cannot reasonably be justified under international law. And supportive allies, while perhaps not strictly necessary to the United States in its recent and foreseeable military campaigns, do make the military option easier to pursue. A war against Iraq would be difficult without access to bases and airspace in countries as diverse as Turkey, Saudi Arabia, Germany, and Canada. For this reason, at least, it would seem to be worth the president’s while to adhere to international law where possible and, where this is not possible, to seek to change the rules.

International lawyers in the Department of State, together with lawyers in other parts of the U.S. government, have excelled in shaping the law to accommodate the interests of the United States. One example, though by no means the only one, concerns the response to the September 11, 2001, terrorist attacks.


There were at least four possible legal justifications available for intervening in Afghanistan.1 First, the United States could have argued that it was acting at the invitation of the Northern Alliance, which could have been cast as the legitimate government of Afghanistan. Second, the United States could have sought explicit authorization from the UN Security Council, which clearly would have been granted. Similarly, the United States could have made a tenable argument that Security Council Resolution 1373, adopted on September 28, 2001, and imposing a range of antiterrorism measures, itself contained authorization for the use of military force. Third, the United States could have claimed a right of unilateral humanitarian intervention based, in part, on the precedent of the 1999 Kosovo intervention. Millions of Afghan lives were at risk from famine during the winter of 2001–02.

None of these arguments were made. Instead, the United States chose to focus on a fourth justification: the right to use force in self-defense against state sponsors of terrorism. This was not the first time this argument was put forward. In 1986, U.S. secretary of state George P. Shultz said:

It is absurd to argue that international law prohibits us from capturing terrorists in international waters or airspace; from attacking them on the soil of other nations, even for the purpose of rescuing hostages; or from using force against states that support, train, and harbor terrorists or guerrillas.2

At the time the claim was widely rejected by other states. When the United States set out to bomb Libya later that year in reliance on the “Shultz Doctrine,” following a terrorist attack on a Berlin nightclub frequented by U.S. servicemen, France and Spain, both NATO allies, inconveniently denied the use of their airspace for the bombing raid.

The international environment in September 2001 was much more conducive to exactly the same claim. Worldwide, there was considerable sympathy for the United States as well as dramatically increased concern about terrorism. Also, governments everywhere were acutely aware of how dangerous it would have been for any country to oppose the United States at that sensitive time.

Support for the claimed right of self-defense was facilitated yet further by evidence linking al-Qaeda to the Taliban government of Afghanistan. This enabled other governments to distinguish between the claimed right to self-defense against state sponsors of terrorism and a more extended claim, namely to a right to use force against terrorists operating within a state that had not actively supported or willingly harbored them. Support was also facilitated by a careful effort to secure it in advance of military action, and not only from individual states, but also from international organizations, including the UN Security Council, NATO, and the Organization of American States.

The Bush administration did not decide to intervene in Afghanistan because of international law. Nevertheless, the decision to intervene and the international environment at that time together presented an opportunity to the lawyers working for the U.S. government to at last secure the Shultz Doctrine, at least insofar as it concerned state sponsors of terrorism, as accepted customary international law.


Weapons of mass destruction (WMD) are a serious problem, but hardly a new one. Poison gas was used repeatedly during the First World War. Two atomic bombs were dropped during the Second World War, and the Cold War was dominated by the colossal potential of the hydrogen bomb. During the last decade, however, two important changes have occurred. First, the U.S. military has become so disproportionately powerful that no rational government would contemplate attacking the United States. Second, an increased threat from nonstate actors—exemplified by the terrorist attacks of September 11, 2001—has raised the prospect that such actors, whom it is difficult to deter, might themselves one day acquire chemical, biological, or nuclear weapons.

As a result of these changes, one can today discern three distinct positions on the law governing preemptive strikes. First, Article 51 of the UN Charter reads:

Nothing in the present Charter shall impair the inherent right of individual or collective self-defense if an armed attack occurs against a Member of the United Nations, until the Security Council has taken measures necessary to maintain international peace and security.

Traditional methods of treaty interpretation focus on the ordinary meaning of the terms. From this perspective, the words “if an armed attack occurs” preclude any right to preemptive self-defense.

Second, it is sometimes argued that preemptive action is justified if there is a “necessity of self-defense, instant, overwhelming, leaving no choice of means, and no moment of deliberation.” These words were written by U.S. secretary of state Daniel Webster in an 1842 letter to Lord Ashburton following the 1837 Caroline incident. In that crisis British forces, claiming self-defense, seized an American steamboat ferrying supplies to a Canadian rebel group, torched it, and sent it over Niagara Falls.3 Until the adoption of the Charter in 1945, Webster’s formulation was widely accepted as the applicable criteria for a limited right of preemptive self-defense in customary international law.

Third, on June 1, 2002, in a commencement speech at West Point, President Bush announced: “We must take the battle to the enemy, disrupt his plans, and confront the worst threats before they emerge.”4 Two months later, in a speech at Fort Drum, New York, he reaffirmed this position: “America must act against these terrible threats before they’re fully formed.”5 There is an important difference between these statements and the criteria articulated by Webster that goes beyond the kinds of threats now being faced. The president made no suggestion of waiting for a “necessity of self-defense” that is “instant, overwhelming, leaving no choice of means, and no moment of deliberation.” He was advocating precautionary rather than preemptive self-defense.

The president’s words must be understood primarily as policy statements, reflecting decisions made without reference to international law. But international lawyers working for the U.S. government would have been tasked with justifying the policy in legal terms, and they must soon have realized that, as expressed, the new policy had little chance of becoming customary international law, even if one accepts the displacement of Article 51. Simply put, most countries do not stand to benefit from an extremely broad right of preemptive self-defense since it would give militarily more powerful states considerable discretion to use force. The absence of a widely reciprocal benefit is usually fatal to the development of customary international law, which requires not only the advancement of a claim but also widespread support or acquiescence.6

The lawyers working for the U.S. government consequently reformulated the policy so as to make it more amenable to others, and thus more effective in promoting legal change. The National Security Strategy of the United States, released on September 20, 2002, explicitly adopts—and then seeks to extend—the criteria articulated by Daniel Webster:

For centuries, international law recognized that nations need not suffer an attack before they can lawfully take action to defend themselves against forces that present an imminent danger of attack. Legal scholars and international jurists often conditioned the legitimacy of preemption on the existence of an imminent threat—most often a visible mobilization of armies, navies, and air forces preparing to attack.

We must adapt the concept of imminent threat to the capabilities and objectives of today’s adversaries.7

The National Security Strategy makes no mention of the UN Charter, thus implicitly asserting that the customary right to self-defense, as it existed before 1945, remains the applicable law today. By glossing over what would normally be a contentious assertion, it strategically seeks to establish a new baseline for the discussion. Only then does the National Security Strategy go further, explicitly asserting that imminence now extends beyond immediate and perilous threats to include more distant and uncertain challenges. The claim is framed in such a way as to seem patently reasonable—provided one accepts the assumption that existing multilateral mechanisms are inadequate to address the threat posed by WMD. The claim is designed to attract support or at least promote acquiescence, and this, combined with a major military action justified on this basis, could well succeed in stretching international law.

Yet the reformulated claim is not as innocuous as it may appear. The National Security Strategy, by reintroducing the Caroline formula and then stretching the criteria of imminence, would introduce greater ambiguity into the law and thus more of a role for power and influence. In short, whether the criteria of imminence are fulfilled would depend in large part on the factual circumstances—as assessed by individual states and groups of states. And the ability of the powerful to influence these assessments will only be enhanced by their ability to claim special knowledge based on secret intelligence. The United States will be able to argue that the criteria are fulfilled whenever it wishes to act militarily, and that they are not fulfilled when others wish to do the same. The law would thus remain available as a diplomatic weapon deployable against others, while the most powerful of states would become free to act as it chose.

Initially, the reformulated claim has met with a skeptical response from a number of countries, including Canada, France, Germany, Mexico, and Saudi Arabia, which refused to countenance an attack on Iraq in the absence of UN Security Council authorization. Only Russia—itself powerful enough not to be worried about force being used against it—expressed support for the claim, while opposing war against Iraq on other grounds. Faced with the prospect of waging a distant and expensive war without many allies, the United States began to look for an alternative way of bringing others on board. As it turned out, the UN Security Council was able to agree on a tough new resolution—in large part because many states were concerned about the detrimental effect that unilateral action would have on the international order.

Security Council Resolution 1441, adopted on November 8, 2002, is a masterpiece of legal drafting that provides ground for all the key players to stand upon. China, France, and Russia can credibly argue that the resolution does not authorize military action and that the United States therefore needs a further resolution before it can lawfully go to war against Iraq. Canada, Saudi Arabia, Turkey, the United Kingdom, and others can credibly argue that the resolution, by expressly applying the concept of “material breach” to resolutions concerning Iraq’s possession of WMD, provides all the authorization they need to support the United States. And the United States, having provided its allies with legal cover, remains able to argue preemptive self-defense—on the basis that it is an inherent right unconstrained by the Charter.

Resolution 1441 will, however, absorb much of the impact that any attack on Iraq has as a precedent in customary international law, since it provides a more widely acceptable justification for such action than preemption. Any subsequent resolution providing even clearer authorization would only exaggerate this effect. One of the potential costs of building coalitions is a reduced ability to reshape customary international law on the back of policy-making. Indeed, the precedent-absorbing character of Resolution 1441 may help to explain its unanimous adoption. Syria, the one council member that was expected to abstain, sees itself as the potential target of a preemptive strike by Israel and is therefore desirous that the right of self-defense remain tightly constrained.

But those who seek strategically to change customary international law adopt a long-term perspective. The Shultz Doctrine took fifteen years to become customary international law—and then only with respect to state sponsors of terrorists who have already attacked the responding state.8 It is to be expected that the United States will continue to press for extensions to the right of self-defense. Indeed, in November 2002 the United States used a Predator drone to kill six terrorist suspects in Yemen and claimed self-defense as its justification. It did so notwithstanding that the much better justification of intervention by invitation was available, since Yemen knew the drone was operating on its territory and approved of the attack.


As the example of the Predator drone in Yemen demonstrates, existing rules of international law provide sufficient scope to enable the United States in cooperation with others to deal with most serious threats. The right to intervene by invitation is based on the undisputed fact that a state can freely consent to having foreign armed forces on its territory. The right of the Security Council to authorize military action is similarly undisputed, and the council, since the end of the Cold War, has demonstrated an appropriately cautious willingness to act. It authorized the 1991 Gulf War, affirmed the U.S. right to self-defense within a day of the terrorist attacks of September 11, 2001, and voted unanimously for Resolution 1441. The only instance where a group of states was willing to take military action to address a serious crisis but found the council deadlocked has been Kosovo, and there most of the intervening states were careful not to advance a legal justification for what was done.9

This raises the intriguing question of whether, in the truly exceptional situation where a serious threat exists, no invitation can be obtained, and the council is not prepared to act, states should simply violate international law without advancing strained and potentially destabilizing legal justifications. States could then allow their action to be assessed subsequently, not in terms of the law, but in terms of its political and moral legitimacy, with a view toward mitigating their responsibility rather than exculpating themselves.

The UN International Law Commission has acknowledged the important role of such mitigating circumstances within its influential 2001 Articles on State Responsibility. When determining whether reparation for a wrongful act is required, the articles suggest, account shall be taken of any contributory “wilful or negligent action or omission” on the part of the injured party.10

Applying this approach to a preemptive (and therefore illegal) strike, evidence of any threat, and of its potential destructive force, would have to be weighed against the preemptive action when determining whether and how much compensation was due. Given that the threat of force is itself a serious violation of international law, the preemptor might fare reasonably well in any such after-the-fact balancing of relative violations. And it is here, with regard to mitigation, that the criteria advanced by Webster in 1842 might best be applied. If there was in fact good evidence of a “necessity of self-defense, instant, overwhelming, leaving no choice of means and no moment of deliberation,” responsibility could well be mitigated and compensation might not even be required. In contrast, if there was time to request the assistance of the Security Council, and such a request was not made, the consequences of the illegality would likely be more severe. Perhaps most important, such determinations could be made after the crisis had subsided, with sufficient time for states—or an international court or tribunal—to investigate and deliberate over what had occurred. And while it might seem counterintuitive that a state that is acting legitimately might have to pay compensation, one would have to question the motives of the state and the gravity of its defensive concerns if the mere possibility of having to pay compensation were sufficient to deter preemptive action.


The provisions of the UN Charter reflect a wide consensus that allowing individual states broad discretion to use force in self-defense would pose a serious threat to the international order and almost every state. For this reason, the extended policy of precautionary action articulated by President Bush in June and July 2002 had little chance of receiving the widespread support necessary for new customary international law.

However, international lawyers working for the U.S. government have seized on the policy initiative as an opportunity to resurrect and extend the limited right of preemptive self-defense that existed before the UN Charter. By doing so, they seek to create greater ambiguity in the law on the use of force, thus allowing more space for the application of power and influence in determining when and where the criterion of imminence applies.

Yet existing international law, in the form of the UN Charter and the customary right of intervention by invitation, is already capable of dealing with most serious threats. For this reason, it bears asking whether it makes sense to change the rules to accommodate the truly exceptional circumstance, or whether an alternative approach of “exceptional illegality” might in fact be preferred. Under such an approach the preempting state would simply violate the law, rather than advance strained and potentially destabilizing justifications, and then allow its claims of political and moral legitimacy to be assessed in mitigation. This approach of exceptional illegality followed by mitigation is not intended to provide an alternative system for regulating the use of force in international affairs. It simply recognizes that circumstances will invariably arise when the existing rules cannot be made to work. In such circumstances, it seems unwise to change longstanding and largely effective rules to accommodate the exception, rather than simply letting the exception prove the rule.


1 For a more detailed analysis, see Michael Byers, “Terrorism, the Use of Force and International Law after 11 September,” International & Comparative Law Quarterly 51 (2002), p. 401
2 George P. Schultz, “Address to the National Defense University, Washington, D.C., January 15, 1986,” International Legal Materials 25 (1986), p. 206.
3 See R. Y. Jennings, “The Caroline and McLeod Cases,” American Journal of International Law 32 (1938), p. 82.
4 “Remarks by President George W. Bush at 2002 Graduation Exercise of the United States Military Academy, West Point, New York,” June 1, 2002; available at
5 “Remarks by President George W. Bush to Troops and Families of the 10th Mountain Division, Fort Drum, New York,” July 19, 2002; available at
6 See, generally, Michael Byers, Custom, Power and the Power of Rules: International Relations and Customary International Law (Cambridge: Cambridge University Press, 1999).
7 “The National Security Strategy of the United States of America September 2002,” p. 15; available at
8 See Michael Byers, “Terrorism, the Use of Force and International Law after 11 September,” pp. 408–409, n. 1.
9 See Michael Byers and Simon Chesterman, “Changing the Rules about Rules? Unilateral Humanitarian Intervention and the Future of International Law,” in J. L. Holzgrefe and Robert O. Keohane, eds., Humanitarian Intervention: Ethical, Legal and Political Dilemmas (Cambridge: Cambridge University Press, 2003).
10 See “Draft articles on Responsibility of States for Internationally Wrongful Acts”, Report of the International Law Commission on the Work of its Fifty-third Session, Article 39; available at

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