In a speech to graduating cadets at West Point in June, President Bush declared, ''America has no empire to extend or utopia to establish.'' When he spoke to veterans assembled at the White House in November, he said: America has ''no territorial ambitions. We don't seek an empire. Our nation is committed to freedom for ourselves and for others.''

Ever since George Washington warned his countrymen against foreign entanglements, empires abroad has been seen as the republic's permanent temptation and its potential nemesis. Yet what word but "empire" describes the awesome thing that America is becoming? It is the only nation that police the world through five global military commands; maintains more than a million men and women at arms on four continents; deploys carrier battle groups on watch in every ocean; guarantees the survival of countries from Israel to South Korea; drives the wheels of global trade and commerce; and fills the hearts and minds of an entire planet with its dreams and desires.

Marines training at Camp Havana, in the desert of Djibouti, where conditions are similar to those they would encounter in Iraq.

A historian once remarked that Britain acquired its empire in ''a fit of absence of mind.'' If Americans have an empire, they have acquired it in a state of deep denial. But Sept. 11 was an awakening, a moment of reckoning with the extent of American power and the avenging hatreds it arouses. Americans may not have thought of the World Trade Center or the Pentagon as the symbolic headquarters of a world empire, but the men with the box cutters certainly did, and so do numberless millions who cheered their terrifying exercise in the propaganda of the deed.

Being an imperial power, however, is more than being the most powerful nation or just the most hated one. It means enforcing such order as there is in the world and doing so in the American interest. It means laying down the rules America wants (on everything from markets to weapons of mass destruction) while exempting itself from other rules (the Kyoto Protocol on climate change and the International Criminal Court) that go against its interest. It also means carrying out imperial functions in places America has inherited from the failed empires of the 20th century -- Ottoman, British and Soviet. In the 21st century, America rules alone, struggling to manage the insurgent zones -- Palestine and the northwest frontier of Pakistan, to name but two -- that have proved to be the nemeses of empires past.

Iraq lays bare the realities of America's new role. Iraq itself is an imperial fiction, cobbled together at the Versailles Peace Conference in 1919 by the French and British and held together by force and violence since independence. Now an expansionist rights violator holds it together with terror. The United Nations lay dozing like a dog before the fire, happy to ignore Saddam, until an American president seized it by the scruff of the neck and made it bark. Multilateral solutions to the world's problems are all very well, but they have no teeth unless America bares its fangs.

America's empire is not like empires of times past, built on colonies, conquest and the white man's burden. We are no longer in the era of the United Fruit Company, when American corporations needed the Marines to secure their investments overseas. The 21st century imperium is a new invention in the annals of political science, an empire lite, a global hegemony whose grace notes are free markets, human rights and democracy, enforced by the most awesome military power the world has ever known. It is the imperialism of a people who remember that their country secured its independence by revolt against an empire, and who like to think of themselves as the friend of freedom everywhere. It is an empire without consciousness of itself as such, constantly shocked that its good intentions arouse resentment abroad. But that does not make it any less of an empire, with a conviction that it alone, in Herman Melville's words, bears ''the ark of the liberties of the world.''

In this vein, the president's National Security Strategy, announced in September, commits America to lead other nations toward ''the single sustainable model for national success,'' by which he meant free markets and liberal democracy. This is strange rhetoric for a Texas politician who ran for office opposing nation-building abroad and calling for a more humble America overseas. But Sept. 11 changed everyone, including a laconic and anti-rhetorical president. His messianic note may be new to him, but it is not new to his office. It has been present in the American vocabulary at least since Woodrow Wilson went to Versailles in 1919 and told the world that he wanted to make it safe for democracy. Ever since Wilson, presidents have sounded the same redemptive note while ''frantically avoiding recognition of the imperialism that we in fact exercise,'' as the theologian Reinhold Niebuhr said in 1960. Even now, as President Bush appears to be maneuvering the country toward war with Iraq, the deepest implication of what is happening has not been fully faced: that Iraq is an imperial operation that would commit a reluctant republic to become the guarantor of peace, stability, democratization and oil supplies in a combustible region of Islamic peoples stretching from Egypt to Afghanistan. A role once played by the Ottoman Empire, then by the French and the British, will now be played by a nation that has to ask whether in becoming an empire it risks losing its soul as a republic. As the United States faces this moment of truth, John Quincy Adams's warning of 1821 remains stark and pertinent: if America were tempted to ''become the dictatress of the world, she would be no longer the ruler of her own spirit.'' What empires lavish abroad, they cannot spend on good republican government at home: on hospitals or roads or schools. A distended military budget only aggravates America's continuing failure to keep its egalitarian promise to itself. And these are not the only costs of empire. Detaining two American citizens without charge or access to counsel in military brigs, maintaining illegal combatants on a foreign island in a legal limbo, keeping lawful aliens under permanent surveillance while deporting others after secret hearings: these are not the actions of a republic that lives by the rule of law but of an imperial power reluctant to trust its own liberties. Such actions may still be a long way short of Roosevelt's internment of the Japanese, but that may mean only that the worst -- following, say, another large attack on United States citizens that produces mass casualties -- is yet to come.

The impending operation in Iraq is thus a defining moment in America's long debate with itself about whether its overseas role as an empire threatens or strengthens its existence as a republic. The American electorate, while still supporting the president, wonders whether his proclamation of a war without end against terrorists and tyrants may only increase its vulnerability while endangering its liberties and its economic health at home. A nation that rarely counts the cost of what it really values now must ask what the ''liberation'' of Iraq is worth. A republic that has paid a tiny burden to maintain its empire -- no more than about 4 percent of its gross domestic product -- now contemplates a bill that is altogether steeper. Even if victory is rapid, a war in Iraq and a postwar occupation may cost anywhere from $120 billion to $200 billion.

What every schoolchild also knows about empires is that they eventually face nemeses. To call America the new Rome is at once to recall Rome's glory and its eventual fate at the hands of the barbarians. A confident and carefree republic -- the city on a hill, whose people have always believed they are immune from history's harms -- now has to confront not just an unending imperial destiny but also a remote possibility that seems to haunt the history of empire: hubris followed by defeat.

EVEN AT THIS late date, it is still possible to ask: Why should a republic take on the risks of empire? Won't it run a chance of endangering its identity as a free people? The problem is that this implies innocent options that in the case of Iraq may no longer exist. Iraq is not just about whether the United States can retain its republican virtue in a wicked world. Virtuous disengagement is no longer a possibility. Since Sept. 11, it has been about whether the republic can survive in safety at home without imperial policing abroad. Face to face with ''evil empires'' of the past, the republic reluctantly accepted a division of the world based on mutually assured destruction. But now it faces much less stable and reliable opponents -- rogue states like Iraq and North Korea with the potential to supply weapons of mass destruction to a terrorist internationale. Iraq represents the first in a series of struggles to contain the proliferation of weapons of mass destruction, the first attempt to shut off the potential supply of lethal technologies to a global terrorist network.

Containment rather than war would be the better course, but the Bush administration seems to have concluded that containment has reached its limits -- and the conclusion is not unreasonable. Containment is not designed to stop production of sarin, VX nerve gas, anthrax and nuclear weapons. Threatened retaliation might deter Saddam from using these weapons, but his continued development of them increases his capacity to intimidate and deter others, including the United States. Already his weapons have sharply raised the cost of any invasion, and as time goes by this could become prohibitive. The possibility that North Korea might quickly develop weapons of mass destruction makes regime change on the Korean peninsula all but unthinkable. Weapons of mass destruction would render Saddam the master of a region that, because it has so much of the world's proven oil reserves, makes it what a military strategist would call the empire's center of gravity.

Iraq may claim to have ceased manufacturing these weapons after 1991, but these claims remain unconvincing, because inspectors found evidence of activity after that date. So what to do? Efforts to embargo and sanction the regime have hurt only the Iraqi people. What is left? An inspections program, even a permanent one, might slow the dictator's weapons programs down, but inspections are easily evaded. That leaves us, but only as a reluctant last resort, with regime change.

Regime change is an imperial task par excellence, since it assumes that the empire's interest has a right to trump the sovereignty of a state. The Bush administration would ask, What moral authority rests with a sovereign who murders and ethnically cleanses his own people, has twice invaded neighboring countries and usurps his people's wealth in order to build palaces and lethal weapons? And the administration is not alone. Not even Kofi Annan, the secretary general, charged with defending the United Nations Charter, says that sovereignty confers impunity for such crimes, though he has made it clear he would prefer to leave a disarmed Saddam in power rather than risk the conflagration of war to unseat him. Regime change also raises the difficult question for Americans of whether their own freedom entails a duty to defend the freedom of others beyond their borders. The precedents here are inconclusive. Just because Wilson and Roosevelt sent Americans to fight and die for freedom in Europe and Asia doesn't mean their successors are committed to this duty everywhere and forever. The war in Vietnam was sold to a skeptical American public as another battle for freedom, and it led the republic into defeat and disgrace.

Yet it remains a fact -- as disagreeable to those left wingers who regard American imperialism as the root of all evil as it is to the right-wing isolationists, who believe that the world beyond our shores is none of our business -- that there are many peoples who owe their freedom to an exercise of American military power. It's not just the Japanese and the Germans, who became democrats under the watchful eye of Generals MacArthur and Clay. There are the Bosnians, whose nation survived because American air power and diplomacy forced an end to a war the Europeans couldn't stop. There are the Kosovars, who would still be imprisoned in Serbia if not for Gen. Wesley Clark and the Air Force. The list of people whose freedom depends on American air and ground power also includes the Afghans and, most inconveniently of all, the Iraqis.

The moral evaluation of empire gets complicated when one of its benefits might be freedom for the oppressed. Iraqi exiles are adamant: even if the Iraqi people might be the immediate victims of an American attack, they would also be its ultimate beneficiaries. It would make the case for military intervention easier, of course, if the Iraqi exiles cut a more impressive figure. They feud and squabble and hate one another nearly as much as they hate Saddam. But what else is to be expected from a political culture pulverized by 40 years of state terror?

If only invasion, and not containment, can build democracy in Iraq, then the question becomes whether the Bush administration actually has any real intention of doing so. The exiles fear that a mere change of regime, a coup in which one Baathist thug replaces another, would suit American interests just as well, provided the thug complied with the interests of the Pentagon and American oil companies. Whenever it has exerted power overseas, America has never been sure whether it values stability -- which means not only political stability but also the steady, profitable flow of goods and raw materials -- more than it values its own rhetoric about democracy. Where the two values have collided, American power has come down heavily on the side of stability, for example, toppling democratically elected leaders from Mossadegh in Iran to Allende in Chile. Iraq is yet another test of this choice. Next door in Iran, from the 1950's to the 1970's, America backed stability over democracy, propping up the autocratic rule of the shah, only to reap the whirlwind of an Islamic fundamentalist revolution in 1979 that delivered neither stability nor real democracy. Does the same fate await an American operation in Iraq?

International human rights groups, like Amnesty International, are dismayed at the way both the British government of Tony Blair and the Bush administration are citing the human rights abuses of Saddam to defend the idea of regime change. Certainly the British and the American governments maintained a complicit and dishonorable silence when Saddam gassed the Kurds in 1988. Yet now that the two governments are taking decisive action, human rights groups seem more outraged by the prospect of action than they are by the abuses they once denounced. The fact that states are both late and hypocritical in their adoption of human rights does not deprive them of the right to use force to defend them.

The disagreeable reality for those who believe in human rights is that there are some occasions -- and Iraq may be one of them -- when war is the only real remedy for regimes that live by terror. This does not mean the choice is morally unproblematic. The choice is one between two evils, between containing and leaving a tyrant in place and the targeted use of force, which will kill people but free a nation from the tyrant's grip.

STILL, THE CLAIM that a free republic may sense a duty to help other people attain their freedom does not answer the prudential question of whether the republic should run such risks. For the risks are huge, and they are imperial. Order, let alone democracy, will take a decade to consolidate in Iraq. The Iraqi opposition's blueprints for a democratic and secular federation of Iraq's component peoples -- Shiites, Sunnis, Kurds, Turkomans and others -- are noble documents, but they are just paper unless American and then international troops, under United Nations mandate, remain to keep the peace until Iraqis trust one another sufficiently to police themselves. Like all imperial exercises in creating order, it will work only if the puppets the Americans install cease to be puppets and build independent political legitimacy of their own.

If America takes on Iraq, it takes on the reordering of the whole region. It will have to stick at it through many successive administrations. The burden of empire is of long duration, and democracies are impatient with long-lasting burdens -- none more so than America. These burdens include opening up a dialogue with the Iranians, who appear to be in a political upsurge themselves, so that they do not feel threatened by a United States-led democracy on their border. The Turks will have to be reassured, and the Kurds will have to be instructed that the real aim of United States policy is not the creation of a Kurdish state that goes on to dismember Turkey. The Syrians will have to be coaxed into abandoning their claims against the Israelis and making peace. The Saudis, once democracy takes root next door in Iraq, will have to be coaxed into embracing democratic change themselves.

All this is possible, but there is a larger challenge still. Unseating an Arab government in Iraq while leaving the Palestinians to face Israeli tanks and helicopter gunships is a virtual guarantee of unending Islamic wrath against the United States. The chief danger in the whole Iraqi gamble lies here -- in supposing that victory over Saddam, in the absence of a Palestinian-Israeli settlement, would leave the United States with a stable hegemony over the Middle East. Absent a Middle East peace, victory in Iraq would still leave the Palestinians face to face with the Israelis in a conflict in which they would destroy not only each other but American authority in the Islamic world as well.

The Americans have played imperial guarantor in the region since Roosevelt met with Ibn Saud in 1945 and Truman recognized Ben-Gurion's Israel in 1948. But it paid little or no price for its imperial pre-eminence until the rise of an armed Palestinian resistance after 1987. Now, with every day that American power appears complicit in Israeli attacks that kill civilians in the West Bank and in Gaza, and with the Arab nations giving their tacit support to Palestinian suicide bombers, the imperial guarantor finds itself dragged into a regional conflict that is one long hemorrhage of its diplomatic and military authority.

Properly understood, then, the operation in Iraq entails a commitment, so far unstated, to enforce a peace on the Palestinians and Israelis. Such a peace must, at a minimum, give the Palestinians a viable, contiguous state capable of providing land and employment for three million people. It must include a commitment to rebuild their shattered government infrastructure, possibly through a United Nations transitional administration, with U.N.-mandated peacekeepers to provide security for Israelis and Palestinians. This is an awesomely tall order, but if America cannot find the will to enforce this minimum of justice, neither it nor Israel will have any safety from terror. This remains true even if you accept that there are terrorists in the Arab world who will never be content unless Israel is driven into the sea. A successful American political strategy against terror depends on providing enough peace for both Israelis and Palestinians that extremists on either side begin to lose the support that keeps violence alive.

Paradoxically, reducing the size of the task does not reduce the risks. If an invasion of Iraq is delinked from Middle East peace, then all America will gain for victory in Iraq is more terror cells in the Muslim world. If America goes on to help the Palestinians achieve a state, the result will not win over those, like Osama bin Laden, who hate America for what it is. But at least it would address the rage of those who hate it for what it does.

This is finally what makes an invasion of Iraq an imperial act: for it to succeed, it will have to build freedom, not just for the Iraqis but also for the Palestinians, along with a greater sense of security for Israel. Again, the paradox of the Iraq operation is that half measures are more dangerous than whole measures. Imperial powers do not have the luxury of timidity, for timidity is not prudence; it is a confession of weakness.

THE QUESTION, then, is not whether America is too powerful but whether it is powerful enough. Does it have what it takes to be grandmaster of what Colin Powell has called the chessboard of the world's most inflammable region?

America has been more successful than most great powers in understanding its strengths as well as its limitations. It has become adept at using what is called soft power -- influence, example and persuasion -- in preference to hard power. Adepts of soft power understand that even the most powerful country in the world can't get its way all the time. Even client states have to be deferred to. When an ally like Saudi Arabia asks the United States to avoid flying over its country when bombing Afghanistan, America complies. When America seeks to use Turkey as a base for hostilities in Iraq, it must accept Turkish preconditions. Being an empire doesn't mean being omnipotent.

Nowhere is this clearer than in America's relations with Israel. America's ally is anything but a client state. Its prime minister has refused direct orders from the president of the United States in the past, and he can be counted on to do so again. An Iraq operation requires the United States not merely to prevent Israel from entering the fray but to make peace with a bitter enemy. Since 1948, American and Israeli security interests have been at one. But as the death struggle in Palestine continues, it exposes the United States to global hatreds that make it impossible for it to align its interests with those Israelis who are opposed to any settlement with the Palestinians that does not amount, in effect, to Palestinian capitulation. The issue is not whether the United States should continue to support the state of Israel, but which state, with which borders and which set of relations with its neighbors, it is willing to risk its imperial authority to secure. The apocalyptic violence of one side and the justified refusal to negotiate under fire on the other side leave precious little time to salvage a two-state solution for the Middle East. But this, even more than rescuing Iraq, is the supreme task -- and test -- of American leadership.

WHAT ASSETS DOES American leadership have at its disposal? At a time when an imperial peace in the Middle East requires diplomats, aid workers and civilians with all the skills in rebuilding shattered societies, American power projection in the area overwhelmingly wears a military uniform. ''Every great power, whatever its ideology,'' Arthur Schlesinger Jr. once wrote, ''has its warrior caste.'' Without realizing the consequences of what they were doing, successive American presidents have turned the projection of American power to the warrior caste, according to the findings of research by Robert J. Lieber of Georgetown University. In President Kennedy's time, Lieber has found, the United States spent 1 percent of its G.D.P. on the nonmilitary aspects of promoting its influence overseas -- State Department, foreign aid, the United Nations, information programs. Under Bush's presidency, the number has declined to just 0.2 percent. Special Forces are more in evidence in the world's developing nations than Peace Corps volunteers and USAID food experts. As Dana Priest demonstrates in ''The Mission,'' a soon-to-be-published study of the American military, the Pentagon's regional commanders exercise more overseas diplomatic and political leverage than the State Department's ambassadors. Even if you accept that generals can make good diplomats and

Special Forces captains can make friends for the United States, it still remains true that the American presence overseas is increasingly armed, in uniform and behind barbed wire and high walls. With every American Embassy now hardened against terrorist attack, the empire's overseas outposts look increasingly like Fort Apache. American power is visible to the world in carrier battle groups patrolling offshore and F-16's whistling overhead. In southern Afghanistan, it is the 82nd Airborne, bulked up in body armor, helmets and weapons, that Pashtun peasants see, not American aid workers and water engineers. Each month the United States spends an estimated $1 billion on military operations in Afghanistan and only $25 million on aid.

This sort of projection of power, hunkered down against attack, can earn the United States fear and respect, but not admiration and affection. America's very strength -- in military power -- cannot conceal its weakness in the areas that really matter: the elements of power that do not subdue by force of arms but inspire by force of example.

IT IS UNSURPRISING that force projection overseas should awaken resentment among America's enemies. More troubling is the hostility it arouses among friends, those whose security is guaranteed by American power. Nowhere is this more obvious than in Europe. At a moment when the costs of empire are mounting for America, her rich European allies matter financially. But in America's emerging global strategy, they have been demoted to reluctant junior partners. This makes them resentful and unwilling allies, less and less able to understand the nation that liberated them in 1945.

For 50 years, Europe rebuilt itself economically while passing on the costs of its defense to the United States. This was a matter of more than just reducing its armed forces and the proportion of national income spent on the military. All Western European countries reduced the martial elements in their national identities. In the process, European identity (with the possible exception of Britain) became postmilitary and postnational. This opened a widening gap with the United States. It remained a nation in which flag, sacrifice and martial honor are central to national identity. Europeans who had once invented the idea of the martial nation-state now looked at American patriotism, the last example of the form, and no longer recognized it as anything but flag-waving extremism. The world's only empire was isolated, not just because it was the biggest power but also because it was the West's last military nation-state.

Sept. 11 rubbed in the lesson that global power is still measured by military capability. The Europeans discovered that they lacked the military instruments to be taken seriously and that their erstwhile defenders, the Americans, regarded them, in a moment of crisis, with suspicious contempt.

Yet the Americans cannot afford to create a global order all on their own. European participation in peacekeeping, nation-building and humanitarian reconstruction is so important that the Americans are required, even when they are unwilling to do so, to include Europeans in the governance of their evolving imperial project. The Americans essentially dictate Europe's place in this new grand design. The United States is multilateral when it wants to be, unilateral when it must be; and it enforces a new division of labor in which America does the fighting, the French, British and Germans do the police patrols in the border zones and the Dutch, Swiss and Scandinavians provide the humanitarian aid.

This is a very different picture of the world than the one entertained by liberal international lawyers and human rights activists who had hoped to see American power integrated into a transnational legal and economic order organized around the United Nations, the World Trade Organization, the International Criminal Court and other international human rights and environmental institutions and mechanisms. Successive American administrations have signed on to those pieces of the transnational legal order that suit their purposes (the World Trade Organization, for example) while ignoring or even sabotaging those parts (the International Criminal Court or the Kyoto Protocol) that do not. A new international order is emerging, but it is designed to suit American imperial objectives. America's allies want a multilateral order that will essentially constrain American power. But the empire will not be tied down like Gulliver with a thousand legal strings.

ON THE NEW imperial frontier, in places like Afghanistan, Bosnia and Kosovo, American military power, together with European money and humanitarian motives, is producing a form of imperial rule for a postimperial age. If this sounds contradictory, it is because the impulses that have gone into this new exercise of power are contradictory. On the one hand, the semiofficial ideology of the Western world -- human rights -- sustains the principle of self-determination, the right of each people to rule themselves free of outside interference. This was the ethical principle that inspired the decolonization of Asia and Africa after World War II. Now we are living through the collapse of many of these former colonial states. Into the resulting vacuum of chaos and massacre a new imperialism has reluctantly stepped -- reluctantly because these places are dangerous and because they seemed, at least until Sept. 11, to be marginal to the interests of the powers concerned. But, gradually, this reluctance has been replaced by an understanding of why order needs to be brought to these places.

Nowhere, after all, could have been more distant than Afghanistan, yet that remote and desperate place was where the attacks of Sept. 11 were prepared. Terror has collapsed distance, and with this collapse has come a sharpened American focus on the necessity of bringing order to the frontier zones. Bringing order is the paradigmatic imperial task, but it is essential, for reasons of both economy and principle, to do so without denying local peoples their rights to some degree of self-determination.

The old European imperialism justified itself as a mission to civilize, to prepare tribes and so-called lesser breeds in the habits of self-discipline necessary for the exercise of self-rule. Self-rule did not necessarily have to happen soon -- the imperial administrators hoped to enjoy the sunset as long as possible -- but it was held out as a distant incentive, and the incentive was crucial in co-opting local elites and preventing them from passing into open rebellion. In the new imperialism, this promise of self-rule cannot be kept so distant, for local elites are all creations of modern nationalism, and modern nationalism's primary ethical content is self-determination. If there is an invasion of Iraq, local elites must be ''empowered'' to take over as soon as the American imperial forces have restored order and the European humanitarians have rebuilt the roads, schools and houses. Nation-building seeks to reconcile imperial power and local self-determination through the medium of an exit strategy. This is imperialism in a hurry: to spend money, to get results, to turn the place back to the locals and get out. But it is similar to the old imperialism in the sense that real power in these zones -- Kosovo, Bosnia, Afghanistan and soon, perhaps, Iraq -- will remain in Washington.

AT THE NEW BEGINNING of the first volume of ''The Decline and Fall of the Roman Empire,'' published in 1776, Edward Gibbon remarked that empires endure only so long as their rulers take care not to overextend their borders. Augustus bequeathed his successors an empire ''within those limits which nature seemed to have placed as its permanent bulwarks and boundaries: on the west the Atlantic Ocean; the Rhine and Danube on the north; the Euphrates on the east; and towards the south the sandy deserts of Arabia and Africa.'' Beyond these boundaries lay the barbarians. But the ''vanity or ignorance'' of the Romans, Gibbon went on, led them to ''despise and sometimes to forget the outlying countries that had been left in the enjoyment of a barbarous independence.'' As a result, the proud Romans were lulled into making the fatal mistake of ''confounding the Roman monarchy with the globe of the earth.''

This characteristic delusion of imperial power is to confuse global power with global domination. The Americans may have the former, but they do not have the latter. They cannot rebuild each failed state or appease each anti-American hatred, and the more they try, the more they expose themselves to the overreach that eventually undermined the classical empires of old.

The secretary of defense may be right when he warns the North Koreans that America is capable of fighting on two fronts -- in Korea and Iraq -- simultaneously, but Americans at home cannot be overjoyed at such a prospect, and if two fronts are possible at once, a much larger number of fronts is not. If conflict in Iraq, North Korea or both becomes a possibility, Al Qaeda can be counted on to seek to strike a busy and overextended empire in the back. What this suggests is not just that overwhelming power never confers the security it promises but also that even the overwhelmingly powerful need friends and allies. In the cold war, the road to the North Korean capital, Pyongyang, led through Moscow and Beijing. Now America needs its old cold war adversaries more than ever to control the breakaway, bankrupt Communist rogue that is threatening America and her clients from Tokyo to Seoul.

Empires survive when they understand that diplomacy, backed by force, is always to be preferred to force alone. Looking into the still more distant future, say a generation ahead, resurgent Russia and China will demand recognition both as world powers and as regional hegemons. As the North Korean case shows, America needs to share the policing of nonproliferation and other threats with these powers, and if it tries, as the current National Security Strategy suggests, to prevent the emergence of any competitor to American global dominance, it risks everything that Gibbon predicted: overextension followed by defeat.

America will also remain vulnerable, despite its overwhelming military power, because its primary enemy, Iraq and North Korea notwithstanding, is not a state, susceptible to deterrence, influence and coercion, but a shadowy cell of fanatics who have proved that they cannot be deterred and coerced and who have hijacked a global ideology -- Islam -- that gives them a bottomless supply of recruits and allies in a war, a war not just against America but against her client regimes in the Islamic world. In many countries in that part of the world, America is caught in the middle of a civil war raging between incompetent and authoritarian regimes and the Islamic revolutionaries who want to return the Arab world to the time of the prophet. It is a civil war between the politics of pure reaction and the politics of the impossible, with America unfortunately aligned on the side of reaction. On Sept. 11, the American empire discovered that in the Middle East its local pillars were literally built on sand.

Until Sept. 11, successive United States administrations treated their Middle Eastern clients like gas stations. This was part of a larger pattern. After 1991 and the collapse of the Soviet empire, American presidents thought they could have imperial domination on the cheap, ruling the world without putting in place any new imperial architecture -- new military alliances, new legal institutions, new international development organisms -- for a postcolonial, post-Soviet world.

The Greeks taught the Romans to call this failure hubris. It was also, in the 1990's, a general failure of the historical imagination, an inability of the post-cold-war West to grasp that the emerging crisis of state order in so many overlapping zones of the world -- from Egypt to Afghanistan -- would eventually become a security threat at home. Radical Islam would never have succeeded in winning adherents if the Muslim countries that won independence from the European empires had been able to convert dreams of self-determination into the reality of competent, rule-abiding states. America has inherited this crisis of self-determination from the empires of the past. Its solution -- to create democracy in Iraq, then hopefully roll out the same happy experiment throughout the Middle East -- is both noble and dangerous: noble because, if successful, it will finally give these peoples the self-determination they vainly fought for against the empires of the past; dangerous because, if it fails, there will be nobody left to blame but the Americans.

The dual nemeses of empire in the 20th century were nationalism, the desire of peoples to rule themselves free of alien domination, and narcissism, the incurable delusion of imperial rulers that the ''lesser breeds'' aspired only to be versions of themselves. Both nationalism and narcissism have threatened the American reassertion of global power since Sept. 11.

AS THE IRAQI operation looms, it is worth keeping Vietnam in mind. Vietnam was a titanic clash between two nation-building strategies, the Americans in support of the South Vietnamese versus the Communists in the north. Yet it proved impossible for foreigners to build stability in a divided country against resistance from a Communist elite fighting in the name of the Vietnamese nation. Vietnam is now one country, its civil war over and its long-term stability assured. An American operation in Iraq will not face a competing nationalist project, but across the Islamic world it will rouse the nationalist passions of people who want to rule themselves and worship as they please. As Vietnam shows, empire is no match, long-term, for nationalism.

America's success in the 20th century owed a great deal to the shrewd understanding that America's interest lay in aligning itself with freedom. Franklin Roosevelt, for example, told his advisers at Yalta in 1945, when he was dividing up the postwar world with Churchill and Stalin, that there were more than a billion ''brown people'' living in Asia, ''ruled by a handful of whites.'' They resent it, the president mused aloud. America's goal, he said, ''must be to help them achieve independence -- 1,100,000,000 enemies are dangerous.''

The core beliefs of our time are the creations of the anticolonial revolt against empire: the idea that all human beings are equal and that each human group has a right to rule itself free of foreign interference. It is at least ironic that American believers in these ideas have ended up supporting the creation of a new form of temporary colonial tutelage for Bosnians, Kosovars and Afghans -- and could for Iraqis. The reason is simply that, however right these principles may be, the political form in which they are realized -- the nationalist nation-building project -- so often delivers liberated colonies straight to tyranny, as in the case of Baath Party rule in Iraq, or straight to chaos, as in Bosnia or Afghanistan. For every nationalist struggle that succeeds in giving its people self-determination and dignity, there are more that deliver their people only up to slaughter or terror or both. For every Vietnam brought about by nationalist struggle, there is a Palestinian struggle trapped in a downward spiral of terror and military oppression.

The age of empire ought to have been succeeded by an age of independent, equal and self-governing nation-states. But that has not come to pass. America has inherited a world scarred not just by the failures of empires past but also by the failure of nationalist movements to create and secure free states -- and now, suddenly, by the desire of Islamists to build theocratic tyrannies on the ruins of failed nationalist dreams.

Those who want America to remain a republic rather than become an empire imagine rightly, but they have not factored in what tyranny or chaos can do to vital American interests. The case for empire is that it has become, in a place like Iraq, the last hope for democracy and stability alike. Even so, empires survive only by understanding their limits. Sept. 11 pitched the Islamic world into the beginning of a long and bloody struggle to determine how it will be ruled and by whom: the authoritarians, the Islamists or perhaps the democrats. America can help repress and contain the struggle, but even though its own security depends on the outcome, it cannot ultimately control it. Only a very deluded imperialist would believe otherwise.

Michael Ignatieff, director of the Carr Center at the Kennedy School of Government, Harvard University, has written recently for The Times Magazine about Bosnia and Afghanistan. He is a contributing writer for the magazine.  

Copyrights 2003 The New York Times Company

Reprinted from the Sunday New York Times Magazine of January 5, 2003.