Author: Mitt Regan

1       Ethical Self-Defense

2       Anticipatory Self-Defense

3       Preventive Self-Defense

4       Assessment

1     Ethical Self-Defense

Some states, most notably the United States (US), have claimed the right to use military force outside of armed conflict against imminent terrorist threats.  The ethical issues related to the use of military force for this purpose are intertwined with assessments of its legal justification.  This is because adoption of the United Nations (UN) Charter in 1945 represented an effort to create an international order that required ethical justification for unilateral state use of force. Such a regime stood in contrast to the previous view that states had an inherent right to resort to war whenever they could advance their interests, such as reducing a perceived threat from another state or strengthening their position relative to other states.

Efforts had been made in the 1920s to regulate recourse to war, but the ethical vision reflected in the UN Charter is that conditions posing a threat to international peace and security are a collective concern that should be addressed by the UN rather than by individual states acting on their own.  Article 2(4) of the Charter thus provides: “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.”

At the same time, the Charter acknowledges the ethical principle that states should be able to protect themselves from harm in certain narrow circumstances. Article 51 provides: “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, until the Security Council has taken measures necessary to maintain international peace and security.”  Notwithstanding a wide variety of scenarios in which states have unilaterally used military force since 1945, all states have almost always felt compelled to justify it as an exercise of self-defense under Article 51. Assessing the ethical propriety of reliance on military force as an element of counterterrorism strategy thus requires analyzing whether a state is using it in accordance with the ethical vision embodied in these two provisions in the UN Charter. It requires, in other words, appreciation of the ethical foundations of institutional arrangements.

The United States has articulated two bases for deploying military force in self-defense against terrorist groups.  The first is that the attacks of 11 September 2001 were acts of war by Al Qaeda.  They inflicted substantial losses on the US, and also demonstrated the capacity and intention of Al Qaeda to engage in additional attacks in the future. The US view is that it therefore is engaged in an ongoing armed conflict with Al Qaeda and its allies, in which it is authorized to use military force against them as combatants who are members of enemy armed forces.

A second rationale for the use of military force in self-defense is that, outside of any armed conflict, the US is authorized to use force against other terrorists who pose an imminent threat to the United States. This theory is based not on an individual’s status as a member of an enemy armed force, but on evidence that a person is engaged in activity that is likely result in an attack on the US unless it is stopped. As such, this person poses an imminent threat to the US, even though it may not be clear when and where a specific attack would occur.  It appears that the US has rarely if ever relied solely on this theory in connection with its targeted killing program.  It therefore has been of most practical relevance since 2013, when the President directed that strikes against persons deemed combatantss in “areas outside of active hostilities” be conducted only if, among other things, a person represents a “continuing imminent threat to US persons.”

The claim of national self-defense based on the existence of an armed conflict with some terrorist groups raises complex issues, but it has gained considerable, if not unanimous, acceptance, at least with respect to certain locations. The second theory, however, has generated much more controversy because of how the US defines an imminent threat. The US position is that the threat of international terrorism requires reconceiving imminence in terms that are not strictly temporal, and that it should not be necessary that a specific attack is in the offing for a threat to be regarded as imminent.  It is enough, rather, that terrorists are regularly engaged in planning attacks that they intend to carry out against the US.  Since the debate over this standard of imminence raises significant ethical issues with respect to counterterrorism, it is the focus of the analysis here.

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2     Anticipatory Self-Defense

A state that purports to use force in self-defense must comply with the principles of necessity and proportionality.  Necessity requires that a state have no means of effectively responding to an attack other than to use force.  It must have exhausted all other means of avoiding the threat, or such alternatives must obviously be futile. Proportionality requires that a state use no more force than necessary to neutralize the threat.  A state thus could not respond with a nuclear missile to an attack on a border post by a small unit of enemy forces.

While Article 51 says that a state may act in self-defense “if an armed attack occurs,” there is general agreement that it need not wait to absorb the first blow before it can use military force.  A state thus may engage in what is known as anticipatory self-defense.  There is some disagreement, however, about how far in advance a state may use force in advance of the actual infliction of force by an attacker.  The disagreement reflects differing assessments of, on the one hand, the need for a state to be able to engage in self-defense that is effective and, on the other hand, the concern that providing states too much discretion increases the risk that they will invoke self-defense as a pretext for aggressive use of military force.

The requirement that an attack be “imminent” is an effort to balance these two ethical concerns.  The classic formulation of imminence is by US Secretary of State Daniel Webster in response to British seizure and destruction of a ship, the Caroline, in US territory that was being used to transport rebels against British rule in Canada back and forth between the US and Canada. Unilateral use of force in self-defense is justified, said Webster, when the “necessity of that self-defence is instant, overwhelming, and leaving no choice of means, and no moment for deliberation.” The implicit analogy is to an individual who is being attacked and has no choice but to resist with force if he or she is to avoid serious harm.  The image of such a scenario aims to reduce the risk of pretextual self-defense by requiring that a state deploy military force only in an emergency.

Even those who accept that a state may act before the first blow lands, however, differ on how soon this may occur.  One view, called the “interceptive” approach, says that a state may act once weapons have been launched.  On this theory, an attack to which a state may respond is imminent at this point.  Such an approach aims to ensure that a state is genuinely responding to an actual threat of harm, rather than simply using force in order to reduce the general risk that another party may pose to it in the balance of power.

Critics of the interceptive approach may be characterized as offering a “preemptive” theory.  They argue that waiting until missiles are actually in the air may be too late for a state to protect itself.  They maintain that an imminent attack should be characterized as one in which another party has taken steps to commit itself to launching an attack.  Such steps may consist of mobilizing armed forces and moving them into positions from which they can be deployed offensively, demonstrating the capability of various weapons systems against a state, declaring belligerent intent, and announcing that no further peaceful means of resolving differences will be pursued.

The preemptive approach differs from the interceptive one in that, unlike a missile that cannot be recalled, these steps are theoretically reversible.  Preemptive theory therefore places considerable emphasis on interpreting the actions of the putative attacking state as a commitment to use force.

This provides a state with more discretion about when it can use force in self-defense than if it is limited to intercepting weapons that actually have been launched. The rationale for this is that waiting for an irreversible commitment to attack by the other side may doom a state’s ability to protect itself. An attack may not have materialized in a definitive physical sense, but a state needs to be able to act effectively if it does.  In keeping with the ethical vision of the UN Charter, advocates of a preemptive theory argue that any more restrictive approach will actually embolden states to use force aggressively because they know that victim states will not be able effectively to resist.  The concern that the opportunity for self-defense be meaningful leads preemptive theorists to place less emphasis than interceptive theorists on temporal proximity as the criterion of imminence.  As one scholar puts it:

“[I]immediacy in relation to anticipatory self-defense is not primarily a question of time, but one of the existence of a credible threat of probable or in exceptional cases potential attack, which together with necessity, the absence of feasible alternatives, make the taking of anticipatory action justifiable or even imperative. While time is a relevant consideration, it is not the only one, nor is it necessarily the most important one.”


This means that factors relevant to imminence may include prior behavior of the putative attacking state; the gravity of the harm that an attack might inflict; the steps that are necessary for a state to mount a defense; whether an attack is likely to come without any observable warning signs; and other contextual considerations. Some theorists suggest, for instance, that the prospect of an attack using weapons of mass destruction might make an attack imminent at an earlier point than would the threat of an attack by conventional weapons.  Whether an attack is imminent therefore depends upon the nature of the threat and ability of a state to defend itself against it.

Even though an attack may be reversible from the standpoint of the potential attacker, the putative victim may only be able to protect itself if it acts by a certain point.

An incident that is widely regarded as an example of justified preemptive self-defense is Israel launching an offensive against Egyptian, Jordanian, and Syrian forces at the start of the Six-Day War in 1967.  While Israel apparently regarded earlier Egyptian low-intensity actions as already instituting a conflict, and anticipatory self-defense was not formally addressed as a justification, it is clear that Israel was the first to mount large-scale military operations far greater than those in which any of the other three states had engaged at that point.

The circumstances that led to the Israeli offensive were that Egypt had closed the Straits of Tiran to all maritime traffic bound for the Israeli port of Eilat; Egypt expelled the UN peacekeeping force stationed in the Sinai Peninsula along the Israeli-Egyptian border and replaced them with Egyptian troops; there was an increase in Fedayeen attacks into Israel from Sinai; Egypt and Syria established a joint command; Egyptian President Nasser delivered speeches in which he declared his intention to permanently end the existence of Israel and “to drive the Jews into the sea”; and Jordan announced its support for Egypt and Syria and entered into a military alliance with those two states.

Israel concluded that an attack from Egypt, Jordan, and Syria was likely in the near future, and that its ability to defend itself against it was crucially dependent on destroying the Egyptian Air Force before these three states launched an attack. As a result, on the morning of 5 June 1967, its air force carried out the destruction of most Egypt’s combat aircraft and air defenses on the ground within a matter of hours. With air superiority thus established, Israeli armed forces drove through the Egyptian positions in the Sinai and reached the Suez Canal, while simultaneously successfully mounting offensives on the Jordanian and Syrian fronts.

While opinion is not unanimous, most states and observers regard Israel’s actions as legitimately taken in self-defense.  As one scholar describes it:  “Egypt, Jordan and Syria had taken a number of steps which clearly pointed to their likely intention and capability to launch an attack – perhaps within a few days – perhaps even sooner or slightly later; but nevertheless within the immediate future.”

As is evident from this example, the preemptive theory of self-defense makes the determination of when a threat is imminent dependent on a wide range of factors that relate to how late a state may act and still be able effectively to defend itself.  While this assessment ideally relies on demonstrable evidence, it inevitably provides an opportunity for a state to claim that it has the best understanding of when it is necessary to act in self-defense. This creates the risk that a state may act on the basis of general anxiety about the strength of its rivals rather than the existence of a concrete threat.  Such behavior would be at odds with the ethical vision of the UN Charter, which is that states collectively, rather than unilaterally, should address balance of power issues that pose a risk to international peace and security.

The interceptive and preemptive conceptions of anticipatory self-defense thus reflect different trade-offs between the desire for a standard that limits the prospect of state opportunism but provides states with a meaningful chance to protect themselves from immediate concrete harm. Both theories, however, are united in their opposition to what has been described as a “preventive” conception of imminence.

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3     Preventive Self-Defense

A third approach to anticipatory self-defense maintains that the use of military force is permissible when conditions exist that are likely if uninterrupted to result in an attack.  The argument is that a specific attack may not be on the horizon, but a variety of events indicate that a party is on the path to eventually launching one.  This theory expands the temporal frame beyond the preemptive approach, which focuses on factors that indicate a definite commitment to a specific attack, but it draws inspiration from that theory’s insistence that a state must be able to attack in time for it effectively to defend itself.

This theory had few adherents until recently, when the US asserted it as an element of its counterterrorism strategy after the attacks of 11 September 2001.  An example of traditional widespread rejection of this theory is the reaction to the June 1981 the Israeli Air Force strike against an Iraqi nuclear reactor under construction located at Osirak near Baghdad. Iraq had obtained the reactor from France in 1975, but it was not yet operational at the time the strike was conducted.  The Osirak facility was subject to International Atomic Energy Agency inspection in accordance with the Nuclear Non-Proliferation Treaty of 1963, but Israel professed reason to believe that Iraq would not permit this and that it was engaged in a program aimed at the production of weapons-grade nuclear material.

The operation destroyed the reactor and killed ten Iraqi soldiers and one French civilian.  Israel claimed that it acted in self-defense.  It said that the reactor had “less than a month to go” before “it might have become critical,” and that “[t]he atomic bombs which that reactor was capable of producing whether from enriched uranium or from plutonium, would be of the Hiroshima size. Thus a mortal danger to the people of Israel progressively arose.” The squad leader said of the operation: “”There was no doubt in the mind of the decision makers that we couldn’t take a chance. We knew that the Iraqis could do exactly what we did in Dimona,” referring to an Israeli nuclear facility widely believe to a site of nuclear weapons development. Israel believed that a successful strike against the facility would be much more difficult once the reactor became operational. It therefore chose to act at what seemed to be the most favorable moment from a military and strategic point of view before the ability to act had been restricted or perhaps even eliminated.

The operation drew widespread condemnation, with critics maintaining that there was no evidence of an Iraqi intention to attack Israel in the foreseeable future, nor that Iraq was even engaged in, much less on the point of developing, a nuclear weapons capability when the attack occurred.  The UN Security Council condemned the attack as a “clear violation of the Charter of the United Nations and the norms of international conduct,” and the UN General Assembly characterized the Israeli action as a “premeditated and unprecedented act of aggression.”  The US voted for the Security Council resolution and temporarily suspended the delivery of four F-16 aircraft to Israel. Such disapproval reflected the view that any potential threat that the reactor might pose to Israel was too remote to be regarded as imminent, and instead depended upon speculation about a chain of future events involving a large set of variables.

In 2002, the United States declared in its National Security Strategy that the rise of international terrorism required rethinking traditional conceptions of imminence.  The Strategy stated: “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.” New threats to security, said the Strategy, require that states “adapt the concept of imminent threat to the capabilities and objectives of today’s adversaries. Rogue states and terrorists do not seek to attack us using conventional means. They know such attacks would fail. Instead, they rely on acts of terror and, potentially, the use of weapons of mass destruction—weapons that can be easily concealed, delivered covertly, and used without warning.”

The Strategy then asserted the US intention to act preemptively to address imminent threats, but with language that suggested reliance on the broader theory of preventive self-defense:

The United States has long maintained the option of preemptive actions to counter a sufficient threat to our national security. The greater the threat, the greater is the risk of inaction— and the more compelling the case for taking anticipatory action to defend ourselves, even if uncertainty remains as to the time and place of the enemy’s attack. To forestall or prevent such hostile acts by our adversaries, the United States will, if necessary, act preemptively.

While the US relied on the claim that its invasion of Iraq in 2003 was justified as enforcement of UN Security Council resolutions regarding weapons of mass destruction that Iraq was violating, many observers regarded it as an operations based on the theory of preventive self-defense that had been announced in the 2002 National Security Strategy.  As a result, the invasion drew widespread criticism in the international community.

The Obama administration avoided pronouncements about the authority to act preventively, but the US has maintained that the concept of “elongated imminence” justifies the use of force against terrorists planning attacks against the US.  It has announced in The White House Report on the Legal Frameworks Guiding the United States’ Use of Military Force and Related National Security Operations (White House Frameworks) Section II-B-3 that the factors it considers in determining if a threat is imminent include:

the nature and immediacy of the threat; the probability of an attack; whether the anticipated attack is part of a concerted pattern of continuing armed activity; the likely scale of the attack and the injury, loss, or damage likely to result therefrom in the absence of mitigating action; and the likelihood that there will be other opportunities to undertake effective action in self-defense that may be expected to cause less serious collateral injury, loss, or damage.

Moreover, “the absence of specific evidence of where an attack will take place or of the precise nature of an attack does not preclude a conclusion that an armed attack is imminent for purposes of the exercise of the right of self-defense, provided that there is a reasonable and objective basis for concluding that an armed attack is imminent.” This is because “certain members of al-Qa’ida (including any potential target of lethal force) are continually plotting attacks; that al-Qa’ida would engage in such attacks regularly to the extent it were able to do; [and] that the US. government may not be aware of plots-as they are developing and thus cannot be confident that none is about to occur.” As a result, “the nation may have a limited window of opportunity within which to strike in a manner that both has a high likelihood of success and reduces the probability of American casualties.”

The references to Al Qaeda are based on the fact that the OLC determined that an Al Qaeda leader who is a US citizen must pose an imminent threat to the US before force can be used against him.  Other members of Al Qaeda may be targeted at any time because they are combatants in an armed conflict with the US.  A claim of self-defense against an imminent threat therefore normally will be relevant with regard to the use of force against members of terrorist groups with which the US is not in an armed conflict, or in instances in which the US chooses to use the imminence standard in targeting members of Al Qaeda and its allies who are US citizens, or in certain geographic areas where such targeting would be politically sensitive.

The United Kingdom and Australia have expressed support for the US conception of imminence, but the theory elsewhere has met with varying degrees of resistance.


One critic suggests that with respect to application of this theory to the threat of a terrorist attack:

The challenge posed in the context of imminence is that, in effect, we are faced with a threat, for which we cannot positively identify how soon it might happen, where it will originate from, where it will strike, or even who precisely will be behind the attack. It is, as such, as far from a specific impending attack as can be.”

Terrorism therefore “raises the question of engaging in self-defence to prevent a possible future attack without knowledge of what it might be. As such, it challenges not so much the interpretation of imminence, but in effect calls into question the very existence of the imminence requirement.” This is because imminence requires demonstration of the need to “respond with urgency to a concrete and known threat that, absent immediate action, is going to materialise into a specific and identifiable attack.” The argument thus is that the notion of “elongated imminence” effectively severs the concept of imminence from any temporal proximity of an attack.

Related to this concern is that a more lenient theory of imminence relaxes the evidentiary burden that a state must bear to justify acting in self-defense.  A state’s assertion that it is likely to be the target of a terrorist attack at some point by some group relies on assessments of intentions and capabilities that are not readily verifiable by other parties.  It thus creates the risk of effectively leaving the determination of whether the use of military force is justified in self-defense solely with the putatively threatened state – precisely a scenario that the UN Charter was designed to avoid.

Finally, critics argue that the existence of terrorist groups that intend to conduct attacks is a legitimate concern, but that it reflects the kind of general threat to international peace and security that should be addressed by collective action through multinational bodies such as the UN. The threat of terrorism poses the risk that terrorist attacks may periodically occur, but limiting the use of military force to self-defense means that a state should be required to identify some definite and concrete threat before it can act unilaterally.  Allowing a state to use force to deal with threats that may be several steps removed from an actual attack would expand the doctrine of self-defense to allow states to address whatever general conditions they regard as threatening – also a scenario that the UN Charter was designed to preclude. Critics of the US conception of imminence suggest that it reflects not so much a revision of the standard of imminence as its elimination.

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4     Assessment

The debate over the requirement of an imminent threat as the precondition for anticipatory self-defense reflects the difficulty that terrorism poses for standards that were developed mainly with conflicts between states in mind.  While not without ambiguity, the concept of imminence in the inter-state context addresses reasonably well the concerns specific to that setting. These are that state intentions can be ambiguous, and that several means are available to resolve conflicts short of the use of force.  A relatively stringent conception of imminence serves to avoid the use of force that may be premature in light of these features of inter-state relations.

With respect to the ambiguity of state intentions, states undertake a variety of actions for a variety of purposes, and may use displays of military force for bargaining purposes or to send messages to other states or to domestic audiences. Responding to this conduct with military force would be precipitous and unleash unnecessary violence. Only the requirement of solid evidence of a likely impending attack avoids this risk.

Second, having commenced activities that could culminate in the use of military force, a state may change its mind for a variety of reasons, such as concessions by another state, the threat of non-forcible sanctions, and assessments of the consequences of using force for its status in the international order and its support from domestic constituents.  Well-developed avenues for peaceful resolution of disputes exist even when conflict seems to loom on the horizon.  This suggests that that we should be cautious in authorizing a state to use force based on its assessment that an attack by another state is imminent without strong evidence of a specific commitment to attack and a concrete threat to the defensive state.

By contrast, the intention of terrorist groups generally is clearer than that of states.  Certain terrorist groups have indicated their intention to attack particular target states.  Such intent is ongoing, with the absence of attacks a function of opportunity and resources rather than a change in aim.  Attacks that are planned may be aborted, but that is likely to be for practical reasons, and it is reasonable to assume that such attacks are delayed rather than simply canceled.  Terrorist groups are thus arguably are akin to states who have declared war and then engage in attacks during that war when they are able to do so, just as one state that declares war and attacks another state may wait until it is propitious to launch additional attacks in the course of that campaign.

Second, there are fewer well-established vehicles for negotiating a peaceful resolution of differences with terrorist groups.  The opportunities will vary, but those groups whose aim is, for instance, to install a global caliphate, or to bring a substantial part of the world under the rule of a religious ideology, are unlikely to be receptive to the type of bargaining that may forestall conflict between states.  This reinforces the sense that such groups are likely to continue to plan and conduct terrorist attacks.

Finally, the evidentiary burden of demonstrating imminence typically is much easier to satisfy with regard to state attacks than terrorist attacks.  States certainly engage in concealment, but observable phenomena such as the movement of ground, sea, and air military assets; statements by public officials; and making defensive preparations often will be available as indicia of an impending attack.  By contrast, of course, terrorists operate in secret, typically do not use conventional military assets in terrorism, and attempt to conceal imminent attacks.

The US argument regarding imminence that is most closely tethered to at least some notion of temporal proximity is the analogy to a victim of domestic violence who kills her abuser while he is asleep.  Courts have been sympathetic to claims that a wife acted in self-defense in some cases in which there was a history of repeated violence that was likely to continue, and the only opportunity the spouse had to eliminate the threat was to act while the abuser is defenseless.  The argument is that the spouse faced an imminent threat of violence despite the fact that there was not such a threat at the time she acted.  Similarly, the US argues, there is a history of terrorist attacks that is likely to continue, the prospect of these attacks poses an imminent threat, and the US should be able to take steps to stop this threat when it has an opportunity to do so.


One response to this argument is that a spousal abuse victim whose defense is accepted is likely to be one whose options are so severely constrained that killing her abuser is the only way to escape further attacks.  By contrast, states have a variety of measures that they can use to attempt to forestall future terrorist attacks, such as police, intelligence, paramilitary and, in some cases, military assets.  States also have the opportunity to coordinate counterterrorism efforts with other states.  They are not automatically doomed to suffer repeated attacks unless they use military force in self-defense against persons who may attack at some point in the future.

A second response is that the possibility that some terrorist attacks will occur in the future may be statistically probable, but this does not mean that an attack is imminent.  It means that states should be vigilant against the possibility of such attacks, but authorizing the use of military force against persons whose activities may eventually culminate in an attack may encourage states to use force to eliminate general risks that are an unavoidable feature of the international order.

International terrorism thus presents a challenge to traditional notions of imminence.  On the one hand, terrorists are plotting attacks in ways that do not provide observable indicia of impending violence until it is often too late to stop it.  On the other hand, using military force at a stage before any attack can be said to be in the offing has the potential to expand the doctrine of self-defense to include threats that may or may not result in an attack.

One approach to taking account of both of these concerns might be to limit self-defense to action against persons who are analogous to state actors who have the authority to organize attacks, and who are irrevocably committed to their perpetuation.  In such cases, there is little chance that, as with states, various diplomatic, economic, or political developments will change the intention to attack.  Imagine, for instance, a military commander who has been given unqualified discretion to launch attacks, and is continuously making plans to do so.  We may say, strictly speaking, that this person represents a standing or a continuous, rather than an imminent threat.  At the same time, he is closely proximate to attacks, and plays a critical role in their occurrence, in a way that others who may contribute to the enterprise are not.  In this respect, he does not represent a vague abstract threat that may materialize into an imminent one.  At the same time, the departure from a traditional conception of imminence may require that a state first try to capture him before being authorized to use lethal force.

A legal memo prepared by the US Department of Justice Office of Legal Counsel (OLC) suggests how these considerations might inform a decision in a particular case.  In authorizing a strike against Anwar Al-Awlaki, a US citizens, the memo said that the evidence supported a conclusion that:

an individual poses an “imminent” threat of violent attack against the United States where he is an operational leader 0f al-Qa’ida or an associated force and personally and continually involved in planning terrorist attacks against the United States. Moreover, where the al-Qa’ida member in question has recently been involved in activities posing an ‘imminent threat of violent attack against the United States, and there is no evidence suggesting that he has renounced or abandoned such activities, that member’s involvement in al-Qa’ida’s continuing terrorist campaign against the United States would support the conclusion that the member poses an imminent threat.

One of the challenges with such an approach is the ability and willingness of a state to provide evidence in support of its determination. States often are able to point to readily observable indicia of another state’s intent to launch an attack, even if there may be disagreement about how to interpret them.  With respect to terrorist attacks, however, a state may not believe that it is in a position to fully disclose its evidence for fear of compromising intelligence sources and methods. Yet without such evidence, other states may be skeptical of the claim of self-defense. There is no easy solution to this problem, but states must realize that their assertion of a right to act in self-defense must be accompanied by as much transparency as possible.

The possible limitation of self-defense to the scenario described above is but one way in which we might try to balance the concerns that surround an attempt to apply the notion of imminence to international terrorism.  It reflects the fact that even more fundamental concerns are the desire on the one hand to ensure that states are able to engage in effective self-defense, and the concern on the other hand to constrain the use of force so that it does not threaten reliance on the international community to respond to threats to peace and security that inevitably arise in that community.  Our assessment of claims to act in national self-defense therefore must be informed by these basic ethical considerations on the institutional level.

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