The United States will likely have to forge a small coalition to deal with North Korea's nuclear program if the current negotiated approach should come up short. This could prove the best way to tackle sanctions, in order to avoid the certain delay and possible Chinese veto in the Security Council that working through the UN would involve. It would be unavoidable if military action were to be taken. Indeed, given the controversial nature of preventive strikes, both as regards the act itself and the risk of retaliation against states near the target, it will almost always be necessary for the United States to create posses for such tasks. The same can be said of special sanctions regimes where something more formal or universal is simply not a realistic option, given the existence of opposition in the Security Council or among major trading partners of the target state. Indeed, the challenge for the United States in its policy toward Iran is to transform what is essentially a unilateral approach into something broader, if still ad hoc.

Obviously, the informal coalition approach is not without its drawbacks. By definition, such groups do not exist before the problem or crisis emerges, and they therefore offer no deterrent effect-although, if formed quickly enough, they can still provide a preventive or preemptive function. But informal coalitions take time to forge and not every protagonist will, like Saddam, provide months for a coalition to get up to speed. They will often lack clear political or legal authority and a means of reliable financing, the absence of which tends to detract from public and international support. The United States will more often than not have to act and provide the bulk of the impetus and resources. And, as is the case with any variant of multilateralism, informal coalitions constrain as well as facilitate. The Gulf War demonstrates that both strategic aims and tactical choices need to be negotiated among members of the coalition.

There are, however, important advantages. The United States has the inherent capacity to create posses where and when it chooses. They do not require much in the way of prior investment. Coalitions of the willing bring with them some of the advantages that derive from collective effort (resources, specialization, diplomatic co-support) without the need for consensus or prearranged authority. They also enjoy some measure of international legitimacy.

More than anything else, though, posses or coalitions of the willing (and able) constitute an approach to international engagement that reflects the basic personality and characteristics of the post-Cold War world. This is a time in history when there are: multiple great powers involved in relationships that resist clear definition and range from the cooperative to the competitive; a growing number of small and medium, sovereign entities; proliferating regional and international bodies, as well as non-governmental organizations; an increasing diffusion of power in all forms; and new sorts of problems (or old problems on a new scale) for which institutions do not yet exist. What is needed as a result is an approach to foreign policy that is inherently flexible, one able to respond to unforeseen situations in unprecedented ways.

The posse approach thus offers a valuable supplement to a world in which regional and international institutions are limited to what they can usefully contribute. Moreover, posses come with the further advantage that they can become more structured and institutionalized if the need and consensus to move in that direction exists. The supplier groups already mentioned reflect this potential, as does the G-7, which over the years has evolved into a quasi-institution for helping to manage a diverse set of political and military, as well as economic, challenges. It may prove possible to adapt or expand the role of other regional or international institutions. Until then, posses can selectively draw on the available assets and resources of such organizations.

Again, though, there will be limits to what we can predict and prepare for. Hence, informal coalitions of the willing increasingly will offer the best vehicle for this country to act effectively in the world when it matters most. Indeed, the real question hanging over the future of this approach to multilateralism is not so much its utility as the willingness of the United States to lead and participate: a posse without a strong sheriff is far more likely to get itself into trouble than to accomplish something of value.