When the dust from the Soviet Union's collapse was still settling, the future of the international system seemed up for grabs. Now that bipolarity has given way to unipolarity, parsing the behavior of the hegemon is clearly the order of the day--and this is the task Andrew Bacevich sets for himself in American Empire. His study is really two books in one. The first, a description of post-Cold War American foreign policy that stresses continuity over change, is impressive and persuasive. The second, an attempt to explain this record with reference to an expansionary logic supposedly inherent in America's domestic political economy, is not.

Bacevich begins by noting how conventional wisdom views the end of the Cold War as a dramatic turning point in the history of American foreign policy. It rendered the country's old grand strategy of containment obsolete, this story runs, forcing policymakers to come up with a replacement appropriate to a new and turbulent era--something they failed to do during the 1990s. Hogwash, he says; in recent years "the United States has in fact adhered to a well-defined grand strategy", which is "to preserve and . . . expand an American imperium." Far from being an improvisation, moreover, this strategy "derives directly from U.S. principles and practices elaborated and implemented during and even before the Cold War."

Bacevich is not the first to make this case, but he does it at length and convincingly. Partisan posturing leads political players on all sides to exaggerate the differences between one administration and the next, he argues, and journalists and historians tend to follow suit, treating each presidency as a distinct and separate phenomenon. But this obscures the broad similarities in approach that lie beneath the surface. Bush, Clinton and Bush fils have all drawn on a common playbook, one that stresses globalization and interdependence as the key features of the contemporary world, free trade and open markets as the chief goals of U.S. policy, and American military hegemony as the guarantor of international stability. The "Big Idea" tying all of this together is

"openness: the removal of barriers to the movement of goods, capital, people, and ideas, thereby fostering an integrated international order conducive to American interests, governed by American norms, [and] regulated by American power."

In support of this thesis Bacevich pulls together a broad range of public statements by officials in all three administrations, showing that there is indeed a consistent rhetorical and ideological core to U.S. foreign policy thinking. And he links this to a basic set of policies, demonstrating that what unites Executive Branch decision-makers from both parties is more significant than what divides them. Only people who do not know the game, therefore, are surprised when their favorite presidential candidate sheds his inflammatory campaign rhetoric about China or Russia or nation-building or whatever and embraces the previous guy's positions once ensconced in office.

Befitting his status as a retired U.S. Army colonel, Bacevich is particularly insightful on military issues, and is an excellent guide to the difficulties the defense establishment has had in coming to terms with the new international environment. Trained and equipped to fight large conventional wars, the American armed forces have instead found themselves pressed into service in a variety of "imperial policing" missions around the globe. As the services fight off attempts at radical military transformation and grumble openly about civilian interference, Washington relies increasingly on modern versions of the "gunboats and Gurkhas" used by imperial powers a century ago. And at the cutting edge of this new/old system are the regional commanders-in-chief, operating as "proconsuls" responsible for the routine management of the Pax Americana.

For help in explaining all of this--most of which he finds distasteful--Bacevich turns to two dissenting historians from decades past, Charles A. Beard and William Appleman Williams. Both have been deservedly pilloried over the years, he says, for botching the great foreign policy issues of their own times, the fights against Nazi Germany and the Soviet Union, respectively. But they are still worth reading, for while they may have been wrong about our enemies, they were right about us. They understood that the true and permanent source of American foreign policy lies within, and cautioned against its all-consuming lust. Looking over their shoulders, Bacevich claims, we can see three great truths about recent events:

"First, that U.S. foreign policy remained above all an expression of domestically generated imperatives; second, that economic expansionism abroad, best achieved by opening the world to trade and foreign investment, was a precondition of America's own well-being and therefore the centerpiece of U.S. strategy; and third, that [officials believed] the cause of peace was best served by the United States' occupying a position of unquestioned global preeminence."

The strategy of "openness" that the United States has recently pursued, therefore, is neither new nor surprising; it merely "adapt[s] the logic of empire to suit the needs of democratic capitalism."

Since contemporary American primacy does indeed raise certain echoes of empires past, a sophisticated theoretical treatment that compared the two would be welcome. Unfortunately, this book is not it. Ignoring the vast literatures on these topics in both diplomatic history and international relations, Bacevich simply replaces one set of naive shibboleths (that American foreign policy is an innocent reaction to outside threats) with another (that it emerges from the machinations of desperate capitalists). In academic terms, he has moved from traditionalism to revisionism without continuing on to the post-revisionist syntheses taught at the end of the semester.

His retrograde theory has two fatal flaws: it explains too little and too much. Bacevich fails to establish clear and convincing links between cause and effect, spending almost no time, for example, tracing the actual process by which domestic economic interests supposedly guide American foreign policy decision-making to outcomes consistent with their preferences. This is odd, since many of the policies he tries to explain--such as the costly interventions in the dirt-poor backwaters of Bosnia, Somalia, Haiti, Kosovo and Afghanistan--have produced no apparent economic benefits.

He also fails to consider why other rich countries today do not display the same neo-imperial drive. Germany and Japan are far more dependent on exports than the United States, so if there were indeed any connection inherent in "democratic capitalism" between internal growth, external markets and expansive foreign policies, the crews on many of the gunboats should be speaking rather different tongues.

That such a simplistic theory turns out to be problematic should come as no surprise, since these and other difficulties have bedeviled similar economic accounts of empire for a century. It is thus no accident, one might say, that the authors whose works Beard and Williams drew on--Hobson, Lenin, Hilferding and the rest, unmentioned in these pages--have long been relegated to the remainder bins. As the German historian Wolfgang Mommsen noted a quarter of a century ago,

"there is no foundation in the old thesis, originally accepted by bourgeois as well as Marxist writers, that expansionist opportunities are necessary to the preservation of capitalism. Indeed the difficulties of the modern world are partly due to the fact that this is not so. The reluctance of private capital to invest in third-world countries is no less notorious than the disinclination of industrialists to consider the economic advantages of the periphery when choosing a site for an industrial plant."

A more satisfying theoretical treatment of America's post-Cold War activities would therefore start by distinguishing among three distinct aspects of the policies in question--their ends, means and scale. Bacevich is right to look inside the country to understand the first--even if his particular economic explanation is wrong. But such solipsistic navel-gazing cannot account for the second and third aspects, which emerge from the interaction between the country and the international system at large.

What Bacevich and many others have a hard time grasping is that America's active role in world affairs has not been a quest for power but a reflection of it. The strong do what they can, Thucydides noted, and the relative strength of the United States has been growing steadily for more than two centuries. Today it is very strong indeed, and in such circumstances the surprise would be not something resembling an American empire, but the modesty and humble isolation that critics so often recommend instead.

Born free, from colonial times onward Americans have rarely doubted that their liberal institutions offered a generalizable template for human happiness and prosperity. Debate has centered primarily on whether to let others discover this on their own or push them to see the light. When the nation was young and relatively weak, it favored a modest view of its mission, protecting and advancing its material interests as necessary, but going not abroad in search of monsters to destroy. As its power grew, however, so did its ambitions, and it began to wonder whether its destiny might involve more than serving as a liberal role model and cheerleader.

By the end of the First World War the United States was the system's strongest player, allowing Woodrow Wilson to use the nation's decisive intervention in the war as a springboard for an attempt to create a global liberal order. His failed efforts left the country chastened, but developments over the next two decades set the stage for a second try. Chief among these developments were the emergence of aggressive tyrannies from the turmoil of the Great Depression, which left American officials further convinced that liberal politics and economics were connected both at home and abroad; and the continued rise in relative U.S. power, which left them better able to translate such thoughts into action.

When the country found itself dragged into war once again, therefore, it embarked on two battles simultaneously. The first was a struggle against the Axis, designed to destroy the regimes that posed an immediate threat. The second was a struggle for a liberal international order, designed to provide the United States and the world with lasting peace and security. Planning for the postwar era was based on the conviction that making the world over in America's image--liberal, democratic, capitalist--would serve everyone. What American policymakers did not foresee was how the Soviet Union would refuse to cooperate, and how a weak and devastated Europe could not be left to fend for itself. If the negative struggle ended in 1945, therefore, America's second, positive struggle continued long after, as it gradually accepted the need to engage the world in order to save it.

The officials who devised the Bretton Woods institutions, the Truman Doctrine, the Marshall Plan, NATO and the remainder of the postwar international architecture never planned to embark on a course of permanent, massive intervention abroad. They wanted and expected their new order to emerge without much effort. In the event, however, the combination of America's burgeoning domestic strength and other nations' weakness inexorably pulled America's interests and commitments outward, and the rest was history.

The record of American foreign policy in recent years has followed precisely the same pattern. Containment proved to be a slow-motion reprise of the negative struggle against the Axis, a battle to rid America and the world of yet another aggressive despotism. And it was complemented during its lifespan by a positive struggle to sustain and expand the ever-more integrated liberal order. The demise of the Soviet Union ended the first struggle, but barely affected the second.

In the 1990s, American policymakers thus found themselves once again adrift in an unexpected and unfamiliar setting. Standing alone at the top of the international system, with no significant challengers to American primacy remaining, their reflexive instinct was to follow the universal logic of the postwar settlement to its natural conclusion, extending the attitudes and institutions of liberal order to the remainder of the globe. Yet no one really knew how long the "unipolar moment" would last, and there seemed little interest at home in spending large amounts of blood and treasure on foreign adventures. The result was the muddling through recounted in Bacevich's pages, as the country's foreign policy establishment tried to keep history rolling forward in its grooves--but without causing anybody, least of all ourselves, too much trouble.

And then came September 11, which changed everything--or did it? In many ways the debate over the "war on terrorism" is déjà vu all over again. Reprising the traditionalist interpretation of the origins of the Cold War, many observers now see the Bush Administration's moves in Afghanistan, Iraq and elsewhere as a simple reaction to a new set of pressing external threats. Others reprise the revisionist stance, arguing that the administration has seized on the attacks as a pretext for doing what it wanted to do anyway, which was to expand its global writ at others' expense. The outcome will be perpetual war for perpetual peace, say these critics, as the new imperialism generates ever-greater resistance from a world unwilling to submit to American domination.

As was true in the earlier debate, each of these perspectives glimpses part of the picture, but neither does justice to what is actually going on. That is because neither adequately addresses the interaction between America's relative power, its ideals and its behavior. Both omit the crucial fact that in the years between the collapse of the Soviet Union and the collapse of the Twin Towers the United States pulled even further ahead of the rest of the pack, becoming in both economic and military terms not just the strongest power in the system but the strongest state in the modern history of international politics. This massive power potential was bound to express itself eventually in a comparably ambitious world role, although just when and how remained to be seen.

In retrospect, therefore, 9/11 may well take its place in the history books alongside the 1950 communist invasion of South Korea, as a catalyst that intensified and militarized a new phase of international politics--this one characterized by American unipolarity. Just as the outbreak of the Korean War gave life and money to a script for postwar order that had been largely written but not yet produced, so the attacks on New York and Washington have galvanized the nation into accepting the lead role in the post-Cold War world that it had previously eschewed. The Bush Administration's much-discussed National Security Strategy, from this perspective, is notable less for its intellectual innovations than for its open (and tactless) proclamation of this new state of affairs. It reflects the new ideological superstructure that follows naturally from the new material base.

So where does this leave us? Neo-traditionalists have trouble accepting that America is indeed now a colossus. Neo-revisionists have trouble accepting that the country's strength can be, and in the past generally has been, a force for good. The truth is that today's officials, like their predecessors half a century ago, are neither innocent heroes nor scheming villains. They are ordinary people in extraordinary circumstances, struggling under enormous pressure to expand the frontiers of a global political and economic order that has, over several decades, helped more people taste freedom and prosperity than in all previous history. Whether they can approach this challenge with appropriate prudence and wisdom, using the immense power at their disposal responsibly so as to replicate their forebears' large successes while avoiding their occasional mistakes, remains to be seen.