The world looks anew at its sole superpower. For the past several years America's most formidable adversary has not been al-Qaeda, North Korea or Iran. The strategic threat to US power has come from rising anti-Americanism. The election of Barack Obama has disarmed it.

Mr Obama's victory this week was no less astonishing for the fact that it was widely predicted by the opinion polls. Everywhere, we have heard the sound of doors slamming on the past; on the bitter legacies of slavery and segregation; on a Republican ascendancy born of the struggle over civil rights and Vietnam; on the Reagan era of unfettered markets; and on the world's deepening disenchantment with Washington.

There are caveats, of course. It should be obvious to all that expectations of Mr Obama are impossibly high. Even so singular a politician will struggle to make the transition from the soaring poetry of the campaign to the workaday prose of government.

Rhetoric will not fix the US economy; or save the planet from climate change. Eloquence will not get US troops out of Iraq; or the Taliban out of Afghanistan. For all that, the simple fact of Mr Obama's victory has changed the geopolitical game.

The world did not have a vote in the US election. It understood, though, that it had a vita interest in the outcome. John McCain had earned the respect of many leaders around the world. But among most electorates, a victory for the Republican candidate would have been greeted with a collective cry of anguish. Instead, many scores of millions have celebrated America's choice.

Some, in Mr Obama's phrase, were huddled around radios in "the world's forgotten corners". They see a president-elect of Kenyan ancestry; a politician whose character was formed by childhood years in Indonesia; and a man whose middle name bears testimony to his Muslim forbears.

Europeans see another Mr Obama. Black, certainly, but a product also of America's familiar east coast: intelligent, urbane and, above all, someone who shares their sensibilities about the necessary balance between power and persuasion in world affairs; Europe's kind of president.

There, you might say, lies Mr Obama's genius: abroad as well as at home, he has proved one of those rare politicians who invites others to discover in him their own priorities and preoccupations.

What his overseas admirers share is a sense that in choosing Mr Obama, the US has rediscovered the virtues and values that long underpinned its moral authority. In recent years, the anti-Bushism born of Iraq, Abu Ghraib and Guantánamo has hardened into visceral anti-Americanism. The election confounds the prevailing image (always something of a distortion) of a nation described only by its arrogance and indifference.

Global goodwill, like well-chosen words, will not solve America's or the world's problems. Tehran is not about to give up its nuclear ambitions nor Moscow its expansionism. Mr Obama takes office, though, with the space to win some of the arguments that were mostly lost by his predecessor even before they were joined.

One of the crueller ironies of George W. Bush's second term is that the president has listened to his critics. The failure of the military adventure in Iraq saw Mr Bush embrace many of the diplomatic strategies urged by his allies. That was evident in negotiations with North Korea and the diplomatic engagement with Iran.

But the effectiveness was blunted by the unshakeable legacy of the first term unilateralism. With Dick Cheney, the vice-president, hovering ever present in the wings, few have believed that the administration's motives could be anything but bad, its embrace of engagement anything but tactical. Mr Bush completely lost the benefit of the doubt.

That will change. It will no longer be possible (it should never have been so with Mr Bush) for America's adversaries to draw moral equivalence between the president of the world's most powerful democracy and tyrants, despots and terrorists everywhere: Mr Obama as the Great Satan?

In demonstrating the infinite capacity of the US to reinvent itself by rediscovering idealism, Mr Obama robs friend and foe of their alibis.

A week ago Moscow's latest threat to site its missiles on Poland's borders might have been greeted with a pained shrug: after all, Russia, many in Europe would have said, had been provoked by Mr Bush.

As it was, the sour response of Dmitry Medvedev, the Russian president, to Mr Obama's victory spoke to his own failure to grasp the significance of the event. Moscow has precious few friends even now. Henceforth it will find it a lot harder to hide its belligerence behind America's unpopularity. The same might be said of Venezuela's Hugo Chavez and one or two others.

There is an important lesson here for Washington's allies, too. Mr Bush has been an excuse for inaction. Many Europeans have spent the past few years carping from the sidelines: the US has been messing things up everywhere, so why should they contribute anything to global security?

That excuse has gone. Before too long, these governments, long too comfortable in their inaction, will have to consider what they have to offer the incoming president in return for America's security guarantees.

Speaking in Chicago's Grant Park, Mr Obama offered his own story as an eloquent answer to the charge that the US has lost the idealism of its founding fathers. He might have added that a world, transfixed by his election victory, gave testimony to the continuing fact of American power. The US has been greatly weakened by Mr Bush's mistakes, but everyone else still looks to Washington to set their foreign policy compass.

That said, the shifting boundaries of geopolitics - the rise of great powers in Asia, the intractable threats from terrorism and nuclear proliferation - leave the US the insufficient, as well as the indispensable, power.

Mr Obama's promise of engagement and collaboration speaks to an intelligence that understands that America needs to gather its friends in order to defeat it enemies; and that the rules of the international system can be enforced on the weakest only if they are observed by the strongest.

The world may be disappointed. One of Mr Obama's most dangerous enemies will be the impatience of our age: the ever present demands that tomorrow's problems be fixed yesterday. Perhaps the new president will lack the decisiveness that is an essential partner to careful deliberation. But this is a moment for optimism. Once in a while, politicians do change the course of history.

By Philip Stephens, The Financial Times, November 6 2008