Prepared for the CEPS/IISS European Security Forum, Brussels, 13 January 2003

Preemptive military action and the legitimate use of force: An American Perspective

by Walter B. Slocombe

"The United States will do what we must to defend our vital interests including, when necessary and appropriate, using our military unilaterally and decisively."
(from the "United States National Security Strategy")

No question has more preoccupied discussions of international law and international relations than that of the legitimacy and wisdom of the use of force. From the "just war" doctrines of the Middle Ages to the Westphalian concept of a sovereign state's "right" to wage war for whatever ends the sovereign judged right to the contorted efforts of 19th Century legal scholars to avoid the problems of the legitimacy of "war" by defining all kinds of military operations as something other than "war" to the futile efforts of the League of Nations and the Kellogg-Briand Pacts to – with various reservations and ambiguities – "outlaw" war to today's discussion of the distinctions between preventive and pre-emptive use of force and the rise of "humanitarian intervention" as a politically correct form of warfare, practical political and military leaders, as well as legal scholars and scholars of international relations, have wrestled with the question of when use of military force is a legitimate instrument of statecraft.

It remains sadly the case that cannon are still the last argument of kings. Not the sincere efforts of leaders and citizens to substitute international institutions and international diplomacy for military power, not the terrible costs of two massive Europe-based world wars, not those of countless smaller internal and international wars throughout the world since 1945, not even the potential consequences of war fought with nuclear, chemical, and biological weapons, as well as the massively increased potential lethality of conventional technology, have fundamentally changed the fact that the threat and use of force are the ultimate instruments of international relations.

Moreover, it is a necessary qualification to the proposition that diplomacy is preferable to force that where vital interests, or at least conflicts over perceived vital interests, are at stake, and where willingness to provide inducements is not unlimited, diplomacy and negotiation are unlikely to succeed unless there is seen to be a real cost to refusal to compromise. The consequences that can be imposed by other means of pressure are puny compared to those of military force. The states (not to mention non-state actors) whose actions are most dangerous and most essential to be constrained are the least likely to be much affected by "international opinion." In such states, the prospects of affecting regime action by appeals to the good sense or innate caution of the citizenry are minimal simply because the regime will have been careful to insulate itself very thoroughly from such public pressures. Even the most powerful international instrument of pressure short of military force – economic sanctions – has a very feeble potential for deflecting such states' actions.[1]

Indeed, it is, in some sense too simple even to say that it is an absolute principle that force is a last resort. Certainly, the risks and costs of military force make it both prudent and moral to refrain from its use while there is a reasonable prospect that other means may be effective. But the principle of using force only after exhausting non-military alternatives necessarily implies a willingness to recognize that, at some point, they have been exhausted, and that waiting too long may mean waiting until military options are no longer effective at acceptable costs.

In the limited time and space available, rather than try to cover the whole huge field, it seems appropriate to focus on two specific questions[2] that have come to the fore in the face of fundamental changes in the international security environment since the end of the Cold War:

Unilateralism, multilateralism, and international decision-makers

Of the two issues, the second, "unilateralism," is relatively the easier, because the dichotomy between "unilateralism" and "multilateralism" is to a large degree an illusory one.

To be sure, there are today a few in the United States who prefer – or at least affect to prefer – unilateral action as a matter of both principle and expediency. They see American military power as so overwhelming that there is no need for the assistance of others. Equally important, they see American purposes as so noble and the perspectives of other governments as so narrow, even craven, that it is not only possible, but necessary, for the United States to ignore their views. The conclusion these "unilateralists by preference" draw is that involvement of other nations in decision-making about American use of force is unwise in that it risks diluting the clarity of American purposes, while involving other nations in actual operations is pointless because they can add nothing significant to American capabilities and including them merely complicates operations.

Conversely, there is a sharply contrary view that decisions on use of military force must always and only be made on a multilateral basis, and indeed, must be made by international institutions, preferably, and perhaps exclusively, by the United Nations. There are some in the United States – and there appear to be many more in other countries – who insist, or at least affect to insist, that only formal approval by the United Nations can legitimate the use of military force, except perhaps in the case of immediate defense by a certifiably innocent victim against direct military attack across a recognized international border by acknowledged forces of a foreign state.

There is, however, in international law – and more in international practice – widespread acceptance of the concept that, in the end, all decisions on use of military force are unilateral, in the sense of being made by nation states, but those decisions must, for reasons of both prudence and principle, be made in the light of the opinions and interests of others so as to gain their support. The great weight of American opinion takes a view that can fairly be described as "unilateral if necessary, but multilateral if possible – and multilateral should almost always be possible."

To begin with the first element – the reservation of the ultimate right of unilateral action – the current US administration is by no means the first to espouse the notion that the United States has the right, even the duty, to act alone if the nation's vital interests are at stake, and that, in the end, it is the United States and no one else that makes that decision. The quotation at the top of this paper is indeed from a National Security Strategy document, but it is drawn from that of President Clinton in 1999, not that of President Bush in 2002.

Nor is the idea that decisions on military force are ultimately national decisions confined to superpowers. Indeed, it seems very likely that, in extremis, every country would take that position. Certainly, even those, like the current German government, who are most enthusiastic in theory for multilateral decisions on use of force, insist on reserving the right to make a separate national decision on whether a multilateral approval of military action is sufficiently justified – or sufficiently serves their own nation's goals and principles – to require actually participating in the action. And there are numerous examples of nations that, in general, regard themselves as adherents of a multilateral approach who proven nonetheless ready to use their military forces for their national aims without bothering much about international opinion, as Spain did last summer over the occupation of a disputed Mediterranean island. To point this out is not accuse Germany or Spain or anyone else of hypocrisy or even to call into question the soundness, much less the sincerity, of their general commitment to multilateral decision-making, but only to observe that it has its limits.

But if unilateralism in theory is all but universal, unilateralism in practice is very hard even for a superpower on a matter of any difficulty. First, in most situations, there may not be much of a practical option of truly unilateral action. American military operations are almost always greatly facilitated by having the cooperation and support of others. The US may have overwhelming capability in many, perhaps most, forms of military power, but the direct military contributions of other nations remain highly useful. The military capability gap is real, but it is not infinite, and many allies can make very helpful contributions, in specialized areas like special operations forces, in capabilities where cutting edge technology is not required, and increasingly also where other nations are, albeit on a smaller scale, approaching American capabilities in fields like precision strike or naval forces. Even setting aside direct military contributions, the United States is, in almost all circumstances, heavily dependent on other countries for bases, overflight rights, and access, and usually for even more direct support in the form of intelligence, cooperation in applying economic and political instruments, and, very importantly, in dealing with the aftermath of conflict. Certainly that was the case in Afghanistan. The Bush Administration's National Security Strategy may exaggerate a little when it says, "There is little of lasting consequence that the United States can accomplish without the sustained cooperation of its allies and friends in Europe," but the basic point is correct – and not just about Europe.

And, of course, there are powerful political and psychological dimensions to international support. America, however patriotic even jingoistic and ostensibly disdainful of foreigners our popular culture, is far from unilateral by preference when it comes to military operations. Opinion polls consistently show – in a variety of contexts – that public support for American military operations is far higher where the United States has the support of its allies than where it would be alone. In part, this reaction is no doubt the sensible one that Americans like others to share the costs and risks, but it also appears to reflect a more complex judgment about international affairs: The American public has more confidence that the decisions of our government are right if they are shared and supported by other countries, as evidenced both by their formal positions and statements and by their willingness to send their own military forces to join in.[3]

Moreover, in most situations, it is not that hard for the United States to garner international support. This is in part the consequence of the obvious fact that the United States has a wide variety of levers of influence and persuasion at its disposal. And the United States need not shy from using those levers. Accepting that the use of military force requires – or is at any rate immensely helped by – international support does not require that the United States be neutral about whether that support is forthcoming. Forced to choose between the United States and its adversaries, most countries will, whatever their misgivings, realize that their interests counsel considering the consequences of opposing the United States on an issue so important to it that the use of military force is an issue.

But the proposition that, in the end, the United States can usually count on the support of those countries that matter does not rest simply – or, I would argue, even primarily – on the proposition that frustrating the Americans would have a price. At bottom, those interests of the United States that plausibly could involve the use of American military force are also the interests of much of the rest of the world. An American diplomacy geared to exhausting non-military alternatives as means of meeting fundamental challenges will, if non-military means fail after being seriously applied, in most cases, also convince many other countries that resort to military force is not only justified, but required in their own interest, not just that of the United States.

However, to say that international support for the use of military force is, in most cases, both necessary and obtainable, is not necessarily to say that the only legitimate source of international support is action by the United Nations. The interesting and much-disputed legal issues of how the UN Charter, in particular Article 51 (reserving the inherent right of individual and collective self-defense against armed attack) should be interpreted – and what, to a practicing lawyer is an equally important issue – who has the legitimate authority to interpret it authoritatively are matters more for scholars than practitioners of international relations.

Of course, formal UN support is desirable, both for its own sake, and for its impact on the actions and attitudes of individual countries whose support may be essential. But insofar as the issue is legitimacy, it is hard to make the case that only UN action suffices. In practice, whether "the United Nations" has given its sanction for use of military force means, as a practical matter, whether there is a Security Council resolution that can plausibly be read as authorizing military force.[4] That, in turn, means whether there is a negative vote by Russia or China. Strictly speaking, of course, the UK or France could also veto, and, in theory, a UN Security Council resolution authorizing the use of military force could fail by reason of not having the affirmative votes of a majority of the Security Council, even if no permanent member voted against it. As a realistic proposition, however, it is indeed hard to imagine a use-of-force situation where a resolution to which none of the "Perm 5" objected enough to use a veto could not get a majority (even if one or more permanent members abstained)- and it is still less plausible that France – not to mention the UK – would exercise a veto in a situation where Russia and/or China would not (always laying aside the – presumably no very unlikely – of a case like Suez in 1956 where the interests of France or the UK were uniquely at issue.) It follows that to require United Nations approval as an absolute condition of legitimate use of military force is to say that no military action of which Russia or China (or, in principle, France, Britain, or, indeed, the US) strongly disapproves is legitimate, no matter how broadly the action is otherwise supported, or how well justified in other international legal or political terms. To illustrate the point – NATO could legitimately point to various UNSC resolutions as supporting its intervention to reverse Milosevic-led Serbia's expulsion of the ethnic Albanian population of Kosovo in 1999. There was, however, no authorizing action by the Security Council in classic "all necessary means" words, and it is not clear that had one been sought, Russia (or China) would have withheld a veto. That intervention was, nonetheless, broadly regarded as legitimate, whether as a "humanitarian intervention" or as a means of forestalling a spreading conflict in a region of Europe that has bred a host of wars in living memory.

Would a failed attempt to get a formal Security Council authorization really have changed things? For most of the world, the Kosovo intervention was legitimate and would still have been so had a UNSC effort produced a veto.[5] For to say that a UNSCR is essential amounts to saying that – not "the international community" – but Russia, China – and, in principle the other permanent members or alternatively, a majority-blocking group of the non-permanent members – are the absolute custodians of the legitimacy of international force. In these terms, the choice between "unilateral" action and "multilateral" is not between a strictly national decision and a UN Security Council Resolution, but one between efforts to garner as much support from other countries as possible, and an insistence, even a preference, for acting alone. In such efforts, the actions of formal regional institutions like NATO and of informal ad hoc groups like the coalition that fought the first Gulf War (admittedly with UNSCR blessing) and may fight a second one, count for as much as a UN Security Council hamstrung by a veto.

Pre-emption: When does the right to self-defense arise?

The question of "pre-emption" is a much more difficult issue. The concept that "defense" is legitimate, while "offense" – more pejoratively "aggression" – is not, lies deep in all discussions of use of military force. In practice, the distinction has always been hard to draw. Indeed, a good deal of effort has been spent – without notable success or general acceptance in practice – in attempting to abolish the distinction by aspiring to abolish force entirely as a means of settling disputes – by a sort of "no fault" renunciation of force. But the principle of "self-defense" has survived, and is, in fact, formally and explicitly recognized in the UN Charter as an "inherent" right, not one created by the Charter.

Lurking in the concept of "self-defense" is the question of at what point the right arises, of where on the spectrum of prevention, pre-emption, and response, military action is justified. The American government has, especially but not exclusively since the attacks of September 11, 2001, stressed the right of pre-emption in certain circumstances, specifically against terrorists and against rogue states threatening to acquire nuclear and other mass destruction weapons.

So far as the United States striking at terrorists is concerned, the issue is hardly one of pre-emption. Once hostilities have been started by others, it is no longer "pre-emption" for the victim to seek to destroy the source, not just to frustrate specific attacks in the future from the same source. The United States has already been – indeed was years before September 2001 – the victim of attack by the coordinated terrorist groups that are the targets for American attacks today. And, beginning at least with the embassy bombings in 1998, the United States was prepared to use force to destroy Al Qaeda operations and leadership where there was sufficient intelligence of their location, entirely independent of any indication that a specific new attack was being planned. There are, to be sure, many difficult legal, moral, political, and practical issues raised by the "war" on terrorism, and by the American determination to, in the words of President Bush's National Security Strategy, "destroy the threat before it reaches our borders." For example, since terrorists are non-state actors, the sovereignty of other countries is, by definition, involved in American attacks on them. Countries in whose territory terrorists are operating have a responsibility to suppress the operations, and the Administration has declared that it will regard countries that give sanctuary to terrorists as subject to military attack just as much as the terrorists themselves. The sovereignty questions raised by this position – and other issues of legality and legitimacy – are real and sometimes difficult issues, but they are not about pre-emption, but about the conduct of a "war" that does not fit traditional patterns.

The Bush Administration has, however, squarely relied on pre-emption in also enunciating a potentially more far-reaching doctrine of anticipatory action against rogue states that are in the process of acquiring nuclear, chemical, and biological weapons. The NSS says, "We must be prepared to stop rogue states ... before they are able to threaten or use weapons of mass destruction against the United States, our allies, or friends." To an important degree, this doctrine is less innovative than either its advocates or its critics profess to believe. Perhaps most important, it is, in its terms, limited to the particular issue of rogue states seeking to acquire WMD; it is not a claim to use force pre-emptively (and unilaterally) whenever the American government judges US interests to be a stake.

Critics, however, argue that the Administration is claiming that self-defense is not limited to "pre-emption" in the sense of forestalling an imminent attack, but "preventive war," in the sense of using military force where the only threat is a vague and uncertain one of possible conflict at some indefinite point in the future. Such "preventive" war, it is argued, is not only in violation of international law, but an unbounded invitation to use of force on mere suspicion of the ambitions or intent of another nation, and indeed an negation of the very concept of international law.

However, far from ignoring international law, the United States government has advanced a sophisticated legal argument for the legitimacy of its position regarding pre-emption against rogue state WMD that is squarely based on international law principles. The argument begins with the proposition that international law unquestionably recognizes a right of self-defense and moreover acknowledges that exercising that right of self-defense does not require absorbing the first blow. As the NSS puts it, under long-recognized international law principles, "nations need not suffer an attack; they can lawfully take action to defend themselves against forces that present an obvious danger of attack."

The classic and widely accepted formulation of that right was stated by Daniel Webster, as American Secretary of State in the 1840's during negotiations about a British cutting out operation in American waters in Lake Ontario against the American ship Caroline that was being used to supply rebels in Canada. He wrote the British Minister, Lord Ashburton, that a nation has a right to act first where the "necessity of self-defense is instant, overwhelming, and leaving no choice of means, no moment for deliberation." The Administration argues that Webster's formulation must be "adapted to the capabilities and objectives of our adversaries." The traditional concept of "imminence" assumed a context where the need for mobilization and other preparation meant that there was a realistic prospect of warning of an attack. Stressing that its claim of a right to pre-empt is limited to action "to eliminate a specific threat to the US or our allies and friends," the Administration argues for a standard of "necessity" that recognizes that terrorists and rogue states with WMD would have at their disposal "weapons that can be easily concealed, delivered covertly, and used without warning." Accordingly, it is lawful to "take anticipatory action to defense ourselves, even if uncertainly remains as to the time and place of the enemy's attack."

On balance, the Administration has the better of the legal argument: Webster's formulation – which was adopted in the course of a protest against, rather than a defense of, a pre-emptive operation and therefore takes a restrictive view – speaks of a "necessity of self-defense" that is "instant, overwhelming," etc. Critics argue that only an immediate prospect of specific attack can met that standard. But, in Webster's formulation, it is the "necessity" that must have those characteristics, and such a necessity may exist without an immediate prospect of attack. The right of anticipatory self-defense by definition presupposes a right to act while action is still possible. If waiting for "imminence" means waiting until it is no longer possible to act effectively, the victim is left no alternative to suffering the first blow. So interpreted, the "right" would be illusory. The Administration is accurate when it points out that once a rogue state has achieved a serious WMD capability, effective action to eliminate the capability may well have become impossible. The problem is not so much that WMD be used with little warning – attacks with conventional weapons have all too often achieved tactical surprise – but that surprise use could be decisive and that the capability can be so successfully concealed that pre-emption is operationally impossible even if warning were available. On this basis, a strong case exists that the right of "self-defense" includes a right to move against WMD programs with high potential danger to the United States (and others) while it is still feasible to do so.[6]

The problems with pre-emption, unfortunately, are not lack of legal legitimacy, but operational practicality. A right of pre-emption is one thing; a meaningful capability to pre-empt is quite another. Exercising the right pre-supposes, both logically and practically, that there is some military operation that will achieve the desired result of eliminating the WMD capability that is targeted at an acceptable cost, taking into account the enemy's possible reactions.

The first operational issue with pre-emption is whether the proposed operation will actually eliminate the WMD capability targeted. The problem is not (usually) whether there is a means of executing a pre-emptive attack once targets are identified, but knowing what and where to strike. Precision weapons require precision intelligence, and pre-emption requires that intelligence be comprehensive as well as precise. Too much attention to action movies and too little to the realities of intelligence collection have tended to obscure the difficulty of knowing enough about a nation's WMD programs to have much confidence of eliminating them by pre-emption. Still more difficult operationally is dealing with what the enemy may do in response, even if his WMD capability has been successfully negated.

The contemporary cases of Iraq and North Korea illustrate the operational problem in some of its dimensions:

In the Korean case, there is no question about the location of the plutonium-production reactor and the re-processing facility at Yongbyon, and, as former Secretary of Defense William Perry has written, the United States military has the capability to destroy them quickly and without causing release of radioactive materials. Such an attack would block the prospect of North Korea extracting some half-dozen bombs worth of plutonium within the next year. But it would not eliminate the North Korean nuclear program, much less Pyongyang's ability to respond with devastating force. Even with regard to North Korea's nuclear programs, the Yongbyon facilities are only part of North Korea's potential. There has been no claim that the United States knows the location of either the plutonium that was extracted in 1991-92 or of the couple of bombs for which that plutonium may have supplied the fissile material. Nor is there a claim that the United States has the detailed knowledge required for high-confidence targeting of other elements of the North Korean program – notably its incipient uranium-enrichment facilities – much less its extensive chemical weapons capabilities. But the real problem with pre-emption in the North Korean case is that the North Korean capability to respond and escalate does not (so far) rest on its WMD, but on its massive conventional forces – and there is no chance that that capability could be eliminated pre-emptively, even by a massive effort. Of course, the problem will only grow worse if North Korea is able to expand its nuclear potential, and at some point, if diplomacy fails, it may be the wiser course to act militarily, accepting the limits on American capability to preempt and relying on deterrence and defense to block or blunt a conventional attack in response. But it is the risks of such a course that have made not just South Korea, but the United States as well, so uneager to press the case for military confrontation.

In a sense, the case for dealing with the Iraqi WMD programs by military force now may be said to be the case for not letting Iraq reach the point Korea is at now. Essentially the argument for eliminating Saddam Hussein's WMD by military force if he will not eliminate it himself under UN monitoring is that, despite the real risks, if the capability is not stopped now, it will be too late – and the world and the region will have to deal with a Saddam regime armed with a powerful WMD capability that can neither be pre-empted nor confidently defended against. But it is significant that the military option being considered against Iraq today is pre-emptive only in the strategic, not the operational, sense. The military option is not to strike at the WMD programs directly but to replace the regime, as the only confident means of eliminating its WMD programs. This is not the product of over-ambition, but of operational reality. Intelligence of a granularity and comprehensiveness necessary for an effective pre-emption limited to the WMD programs themselves is no more available in the Iraqi than the Korean case. Indeed, in the Iraqi case there is not even an equivalent to Yongbyon, that is, a single key facility whose destruction is military feasible and would at a stroke deeply set back the WMD efforts. It is this lack of a military option able to eliminate the WMD that makes a campaign to oust the regime the only military option if UN disarmament efforts fail. Happily, Saddam Hussein has less formidable responsive options than does Kim Jong Il because his military is relatively weak and his ability to strike rapidly at high value targets is much less. The American assessment is that none of his potential responses is anything like as significant as the North Korean potential to wreak immense destruction on South Korea, and that the risks entailed by what he can do can be reduced to acceptable levels – and are in any event better run now that faced later when his WMD programs are far more developed. But Iraq has some potentially very destructive responses, and their potential use is a major complication for military planning – and a major source of the reluctance to many to support an invasion.

In short, the contrasting cases of Iraq and North Korea today may be said to illustrate both the conceptual strength of the administration's doctrine of pre-emption against rogue state WMD, and its limitations in practice. There will, unfortunately perhaps, still be plenty of scope for military operations and capabilities aimed at deterrence and for defense if deterrence fails.


[1] "Covert" action is similarly not often a viable alternative to military force. In any event, used on a significant scale, "covert" action is use of force, though perhaps delivered through a different state agency and with different methods.

[2] This limitation leaves out several issues that have in the United States been major elements of the discussion of use of force – including the magnitude of American interest sufficient to justify use of military force and the degree of popular support required (and the closely related question of the relative roles of Congress and the President in domestic US decisions on use of force). Suffice it to say, as to the first, that only important interests justify military action, but many interests are "important" in this sense without involving immediate direct threats to the US homeland. As to the second, no democracy, and certainly not the United States, can fight a war on any scale without public and parliamentary support, but where there is clear national interest and a coherent strategy for advancing it and a convincing rationale for using force to do so, the American public is prepared to sustain significant burdens and run significant risks, and Congress is prepared to support the Executive branch, or at any rate to acquiesce in its decisions.

[3] The political/psychological importance of other countries' direct military participation has an effect that – perhaps fortunately for the United States – the contributors may not fully realize: Those countries that do provide forces to US-led military operations, however much they may have to defer to US leadership of the overall direction of the military operation, can absolutely reserve a veto over what their own forces do – and at the same time exert an influence on American military and, still more, on American political decision-making related to the conflict out of all proportion to the objective significance of their military contributions.

[4] During the Cold War, when the USSR could be relied on to veto any UNSCR it deemed inconsistent with its interest, the United States argued that a "uniting for peace" resolution of the General Assembly could carry the same UN authority. With the changes in the composition of the General Assembly making it very hard to assemble a GA majority – and the end of the Cold War confrontation with Russia making it more possible to get Perm 5 consensus – this doctrine has fallen into desuetude.

[5] To be sure, some take the position that the Kosovo operation was "proper" because it served legitimate international purposes but not "lawful," because it was not explicitly authorized by a UN Security Council resolution. That a distinction that says more about attitudes toward "international law," than about norms of international conduct.

[6] In the particular case of Iraq and North Korea, of course, there may be an entirely independent legal basis for action that each is in breach of its obligations as a party to the NPT (and in both cases also of other commitments not to have or seek nuclear weapons). It is certainly arguable that other states are entitled to resort to force to compel compliance with such obligations.