By now it is apparent that a significant change has occurred in the view taken of American power. Whereas before September 11, 2001, there was an abundance of articles and books on the brief life of American hegemony, in the aftermath of that event they have radically declined in number. What the Gulf War failed to do, the war in Afghanistan succeeded in doing. It has made converts (however reluctant) of most of those who before were skeptics, not so much of the fact of American hegemony today but of its durability.  The "unipolar moment", to use Charles Krauthammer's terminology, has become the "unipolar era."  Years have been replaced by decades.

Although not a federal state today--perhaps ever--Europe nevertheless has a collective weight that rivals the United States in trade and finance. In defense, Europe is forging a common policy and acquiring the means to act on its own. A new center of global power is thus in the making.  Yet, at present, the states that make up the EU possess resources sufficient to rival the United States. In what period of time they might succeed in converting that potential power into usable power is anyone's guess. One need not be a Euroskeptic to see the process taking at least several decades. If demographic trends unfold as they are now projected, that day may never come. In any event, the EU's challenge is above all dependent upon forging a centralized decision-making body having the authority to act on behalf of Europe in matters of foreign policy, and this would of course mean the surrender by the separate states of control over foreign policy. The European response to Iraq has shown that the EU is still a long way from achieving so revolutionary a change, and, with its expansion to include ten new member states, that day is even more distant. In its absence, American domination of the continent may be expected to continue into an indefinite future, particularly if the Bush Administration's National Security Strategy prevails. The NSS is designed to widen still further the immense gap in military spending and capability that exists today between the United States and any other nation or feasible combination of nations.  If the end of the American era is to come in the foreseeable future, it will therefore have to result largely from internal causes.  We did need a major adversary to draw us into the role we now play, and prior to September 11, 2001 a growing aversion to bearing the costs of hegemony in the absence of a major adversary was indeed apparent. Still, that aversion did not lead the nation to abandon its pretensions to an order-giving role. Having once gained the commanding position we came to occupy, we were reluctant to give it up.  

Although the long-term effects terrorism will have on American policy necessarily remain speculative, it seems odd to insist that they must reinforce both unilateralism and isolationism. The case for believing that they must reinforce unilateralism is reasonably clear and follows from the administration's conception of the threat and particularly the strategy for combating it. As spelled out in the administration's National Security Strategy, the threat terrorists and rogue states pose arises from the marriage of radicalism and technology. The result is a security environment more complex and dangerous than that of an earlier era. In the Cold War, the United States faced a risk-averse adversary; traditional concepts of deterrence worked. Against terrorists and rogue states, however, the former constraints are no longer effective. For them, weapons of mass destruction have been transformed from weapons of last resort to weapons of choice. It is in these changed circumstances that a strategy of pre-emption is both necessary and justified. The concept of imminent threat, says the administration, must be adapted to the capabilities and objectives of today's adversaries.  

Although nothing lasts forever, the only safe bet is that the international system will remain unipolar for a long time. It may well be that American power will go without serious challenge until the middle of this century. In these circumstances, what constraints should the holders of such power observe? The answer given by the Bush Administration seems simple enough.  This government alone, it declares, will determine when and for what purposes force should be employed, and it will do so according to its own distinctive standards of judgment. That the decision is unilateral does not necessarily mean that action will also be unilateral. Other states may join in, whatever their reasons for becoming part of the "coalitions of the willing." It may be that a given action will bear the imprimatur of the UN Security Council, or not. Should it do so, the American government would be particularly gratified. Nevertheless, the source and legitimacy of the action will remain independent of the United Nations.  This has been the position of the Bush Administration in the case of Iraq.  Should it become the position of future administrations as well, the United States will set itself against world opinion and its own best traditions.  What the world apparently fears most is neither terrorists nor tyrants but the untrammeled power of the United States. If this nation is to lead, it will first have to reassure the world about the uses and purposes of its power.

Robert Tucker is professor emeritus of American foreign policy at The Johns

Hopkins University.