But what precisely is coming to an end? Neoconservatism in all its pomp conceived - in the Project for a New American Century - that, following the collapse of the Soviet Union, the world could be remade in the American image, that the previous bipolar world could be replaced by a unipolar one in which the US was the dominant arbiter of global and regional affairs. In fact, the Bush administration never came close to this. For a short time it did succeed in persuading the great majority of countries to accept the priority of the war against terror and seemingly to sign up for it: even the intervention in Afghanistan, in the aftermath of 9/11, elicited widespread acquiescence. But the US singularly failed to command a majority of states in support of the invasion of Iraq and garnered even less support when it came to global public opinion. It demonstrated its unilateral intent by ignoring its failure to gain assent within the UN and invading Iraq, but the subsequent failure of its Iraqi adventure has served only to reinforce its isolation and demonstrate the folly of its unilateralism. Its strategy in the Middle East - always the epicentre of the neoconservative global project - lies in tatters.

Elsewhere the neoconservative project was stillborn. North Korea was branded as part of the "axis of evil" but the US, in agreeing to the six-party talks as a way of handling the crisis on the Korean peninsula, tacitly admitted that it simply did not enjoy enough leverage to deal with the Kim regime. This was demonstrated more forcibly with its failure to prevent the recent nuclear test, and the US's subsequent dependence on China for seeking some means of engaging North Korea in dialogue. In fact China has now cajoled the US into accepting the need for it to do something it had previously resisted: entering into direct talks with North Korea, with China playing the role of honest broker. For all the neoconservative bluster, the US is simply too weak in east Asia - and China too strong - for it to be anything other than a secondary player in the North Korean crisis. It has been a striking illustration of the slow, remorseless decline of American influence in the region.

Meanwhile, in the region that it has dominated for well over a century, which it has traditionally regarded as its own backyard and in which it intervened with impunity throughout the cold war - namely Latin America - the US is now facing its bleakest ever situation, far worse than anything the Cuban regime represented during the cold war. The US is confronted with a formidable and well-resourced adversary in Chávez's Venezuela, and a continent in which the left has made extraordinary progress. The Bush administration, so far at least, has been quite unable to halt its growing isolation in Latin America and the left's onward march.

Even in the Middle East, the weakness of the neoconservative position has become increasingly evident in its handling of Iran, another member of the "axis of evil". As in the case of North Korea, the US, partly as a result of its preoccupation with the occupation of Iraq, in effect devolved negotiations over Iran's nuclear ambitions to the group of four consisting of Germany, France, Russia and the UK.

Although the west Europeans have been happy to do most of America's bidding, Russia has not and nor, it would appear, has China. Both are permanent members of the UN security council, and both are resistant to sanctions and the threat of military action. As a result, negotiations over Iran have been mired in something of an impasse. Of course, if the neoconservatives had felt strong enough, they could have forced the issue in a manner similar to their approach in Iraq. The point is that they did not. And now it would seem inconceivable that they can contemplate military action against Iran.

On the contrary, the tables appear to be in the process of being turned: the US, instead of seeking to isolate Iran, is now likely to need Iranian and Syrian support in helping to sort out the debacle in Iraq. Taken with the failure of the Israeli invasion of Lebanon and the continuing disaster of the occupied territories, we can see that the US is in retreat. Ever since 1956, it has been increasingly and formidably dominant in the region, with Israel riding pillion, and since 1989 it has been the overwhelming arbiter of events there. This year marks the beginning of the decline of American power in the Middle East, with untold consequences.

Here we can see the cost of Bush's adventurism for American imperial power. In failing to understand the inherent limits of US global power consequent upon deeper, though seemingly unrecognised, longer-term global trends, the Bush administration hugely overestimated American power and thereby committed a gross act of imperial over-reach, for which subsequent administrations will pay a heavy price. Far from the US simply conjoining its pre-1989 power with that of the deceased USSR, it is increasingly confronted with a world marked by the growing power of a range of new national actors, notably - but by no means only - China, India and Brazil.

Just six years into the 21st century, one can say this is not shaping up to be anything like an American century. Rather, the US seems much more likely to be faced with a very different kind of future: how to manage its own imperial decline. And, as a footnote, one might add that this is a task for which pragmatists are rather better suited than ideologues.

· Martin Jacques is a visiting research fellow at the Asia Research Centre, London School of Economics

Martinjacques1@aol.com