The years immediately following the end of the Cold War offered a tantalizing glimpse at a new kind of international order -- one in which nations would grow together or disappear altogether, ideological conflicts would melt away and cultures would intermingle through increasingly free commerce and communications.

It was the end of international competition, the end of geopolitics, the end of history. The liberal democratic world wanted to believe that the conclusion of the Cold War did not end just one strategic and ideological conflict but all strategic and ideological conflict. In the 1990s, under George H.W. Bush and Bill Clinton, American strategy was aimed at building a post-Cold War order around expanding markets, democracy and institutions -- the triumphant embodiment of the liberal vision of international order.

But it was all something of a mirage. We now know that both nationalism and ideology were already making a comeback in the 1990s. Russia quickly lost its desire to be part of the liberal West. China had embarked on a course of growing ambition and military power. The forces of radical Islam had already begun their jihad, globalization had already caused a backlash around the world and the juggernaut of democracy had already stalled and begun to tip precariously. Yet even today many cling to the vision of "a world transformed."

The world has not been transformed. Nations remain as strong as ever, and so too the nationalist ambitions, the passions and the competition among nations that have shaped history. It's true that the world is still "unipolar," and the United States remains the only superpower. But international competition among great powers has returned, with the United States, Russia, China, Europe, Japan, India, Iran and others vying for regional predominance. Struggles for power, influence, honor and status in the world have once again become key features of the international scene.

Ideologically, this is a time not of convergence but of divergence. The competition between liberalism and autocracy has reemerged, with the nations of the world increasingly lining up, as in the past, along ideological lines. Finally, there is the fault line between modernity and tradition, the violent struggle of Islamic fundamentalists against the modern powers and the secular cultures that, in their view, have penetrated and polluted the Islamic world.

Many still prefer to believe that the world is in turmoil not because it is in turmoil but because President Bush made it so by destroying a new, hopeful era. And when Bush leaves, they believe, it can return once again to the way it was. Having glimpsed the mirage once, people naturally want to see it and believe in it again.

The first illusion, however, is that Bush really changed anything. Historians will long debate the decision to go to war in Iraq, but what they are least likely to conclude is that the intervention was wildly out of character for the United States. Since the end of World War II at least, American presidents of both parties have pursued a fairly consistent approach to the world. They have regarded the U.S. as the "locomotive at the head of mankind," to use Dean Acheson's phrase. They have amassed power and influence and deployed them in ever-widening arcs around the globe on behalf of interests, ideals and ambitions both tangible and intangible.

Since 1945, Americans have insisted on acquiring and maintaining military supremacy -- a "preponderance of power" in the world -- rather than a balance of power with other nations. They have operated on the ideological conviction that liberal democracy is the only legitimate form of government and that other forms are not only illegitimate but transitory. They have seen the United States as a catalyst for change in human affairs.

When people talk about a Bush Doctrine, they generally refer to three sets of principles -- the idea of preemptive or preventive military action; the promotion of democracy and "regime change"; and a diplomacy tending toward "unilateralism," a willingness to act without the sanction of international bodies such as the United Nations Security Council or the unanimous approval of its allies.

But these qualities of U.S. foreign policy reflect not one man or one party or one circle of thinkers. They spring from the nation's historical experience. They are underpinned, on the one hand, by old beliefs and ambitions and, on the other, by power. As long as Americans elect leaders who believe it is the role of the United States to improve the world, they are unlikely to abjure any of these tools. And as long as American power in all its forms is sufficient to shape the behavior of others, the broad direction of American foreign policy is unlikely to change.

Since the end of the Cold War and the emergence of this unipolar world, there has been much anticipation of the rise of a multipolar world in which the U.S. is no longer predominant. Many have argued the theoretical and practical unsustainability, not to mention undesirability, of a world with only one superpower. Mainstream realist theory has assumed that others must inevitably band together to balance against the superpower.

Yet American predominance persists. The enormous and productive American economy remains at the center of the international economic system. American democratic principles are shared by more than 100 nations. The anticipated global balancing has for the most part not occurred. Russia and China certainly share a common and openly expressed goal of checking U.S. hegemony, but there has been no concerted or cooperative effort at balancing. The two powers do not trust one another and are traditional rivals. The rise of China inspires at least as much nervousness in Russia as it does in the United States. In any case, China and Russia cannot balance the United States without at least some help from Europe, Japan, India or at least some of the other advanced, democratic nations. And those powerful players are not joining the effort.

Nor has the Iraq war had the effect expected by many. Although there are reasonable sounding theories as to why the U.S. position should be eroding as a result of global opposition to the war and the unpopularity of the current administration, there has been little measurable change in the actual policies of nations, other than their reluctance to assist the U.S. in Iraq. In 2003, those who claimed the U.S. global position was eroding pointed to electoral results in some friendly countries: the defeat of Jose Maria Aznar's party in Spain, for example, and the election of President Luiz Inacio Lula da Silva in Brazil. But if elections are the test, other, more recent, votes have put relatively pro-American leaders in power in Berlin, Paris, Tokyo, Ottawa and elsewhere.

The world's failure to balance against the superpower is the more striking because the United States, notwithstanding its difficult interventions in Iraq and Afghanistan, continues to expand its power and military reach. The American defense budget currently comes in at roughly $500 billion a year, not including supplemental spending totaling more than $100 billion on Iraq and Afghanistan.

Predominance, of course, is not the same thing as omnipotence. Just because the United States has more power than everyone else does not mean it can impose its will on everyone else. American predominance in the early years after World War II did not prevent the North Korean invasion of the South, a communist victory in China or the consolidation of the Soviet empire in Eastern Europe -- all far greater strategic setbacks than anything the United States has yet suffered or is likely to suffer in Iraq and Afghanistan.

By the same token, though, foreign policy failures do not necessarily undermine predominance. Some have suggested that failure in Iraq would mean the end of predominance and unipolarity. But a superpower can lose a war -- in Vietnam or in Iraq -- without ceasing to be a superpower if the fundamental international conditions continue to support its predominance. As long as the U.S.remains strong -- and as long as potential challengers inspire more fear than sympathy among their neighbors -- the structure of the international system should remain as Chinese strategists now describe it: one superpower and many great powers.

This is a good thing, and it should continue to be a primary goal of American foreign policy to perpetuate this relatively benign international configuration of power. The unipolar order, with the United States as the predominant power, is unavoidably riddled with flaws and contradictions. It inspires fears and jealousies. The United States is, like all other nations, not immune to error. Compared to the ideal Kantian international order, in which all the world's powers would be peace-loving equals conducting themselves wisely, prudently and in strict obeisance to international law, the unipolar system is both dangerous and unjust.

Compared to any plausible alternative in the real world, however, it is relatively stable and less likely to produce a major war between great powers. It is also comparatively benevolent, from a liberal perspective, and more conducive to the principles of economic and political liberalism that Americans and many others value.

American predominance, therefore, does not stand in the way of progress toward a better world. It stands in the way of regression toward a more dangerous world. The choice is not between an American-dominated order and a world that looks like the European Union. The future international order will be shaped by those who have the power to shape it. Its leaders will not meet in Brussels but in Beijing, Moscow and Washington.

After World War II, another moment in history when hopes for a new kind of international order were rampant, Hans Morgenthau warned idealists against imagining that at some point, "the final curtain would fall and the game of power politics would no longer be played."

The world struggle continued then, and it continues today.

Six decades ago, American leaders believed the United States had the unique ability and the unique responsibility to use its power to prevent a slide back to the circumstances that produced two world wars and innumerable national calamities.

Although much has changed since then, America's responsibility has not.

Robert Kagan is a fellow at the German Marshall Fund and a senior associate at the Carnegie Endowment for International Peace. A longer version of this article appears in the August/September issue of Policy Review.