Why has the United States coped so badly with the aftermath of the Iraq war? How could it have been so apparently unprepared for the chaos that followed Saddam Hussein's defeat? And why, on the most concrete level, did it have no "exit strategy" to follow the invasion?

Those who opposed the war recite these questions with delighted sanctimoniousness, believing that their simple iteration proves the justice of the original anti-war case.

But for those of us who supported (and still support) the American action, these are not rhetorical matters. It is urgently important to understand what followed the collapse of tyranny in Iraq, and why the American strategy seemed to have no plan for dealing with it.

The American "mistake" - if mistake it is - is a generous and well-intentioned one: it assumes that, because freedom is a natural right (a belief that is fundamental to American political culture), then it must also be a natural condition.

To Americans of all persuasions and parties, personal liberty is an absolute and inviolable good: it is the state to which all human beings instinctively strive.

When George Bush describes the forces he is fighting as "the enemies of freedom", he means that they are the enemies of all that makes life worth living. What follows from this is that, given a choice, all peoples in all places and times will choose freedom over oppression. And so it was assumed that, in Iraq, liberation would be enough.

To be released from a murderous tyranny would naturally result in an embrace, not necessarily of smooth-running modern democracy, but of the possibilities of emancipation and individual opportunity.

It is worth remembering that - given the existence of an educated Iraqi political class, much of which had been living in exile but affirmed its desire to return - this idea seemed particularly credible.

Indeed, America had seemed to be taking a much greater gamble on this philosophy in Afghanistan, for which it received far less criticism, perhaps because countries such as France and Russia did not have the same vested interest in the survival of the Taliban regime as they had in Saddam's.

Richard Perle, an influential Washington neo-conservative, said last week that it had been an error to "allow liberation to turn into occupation". In other words, America never wanted, or intended, to run the place.

Contrary to left-wing myth, America is not a neo-colonialist country: it has no interest in creating a new imperium. The national temperament is, if not always isolationist, at least chronically inward-looking and self-absorbed.

Few things could appeal less to the American populace (and consequently to its populist political leaders) than conquering foreign lands and administering remote territories.

The American predilection is overwhelmingly for tending its own garden - getting on with its favoured domestic pastimes of creating wealth and cultivating private satisfactions.

This disinclination to run, and exploit, far-flung bits of the world is difficult for Europeans, who were historically addicted to colonialism, to comprehend.

That is why they so often make fatuous assertions about American intentions: that the US wanted to invade Iraq to "grab the oil", for example.

To misunderstand the fundamental idealism - and perhaps naivety - of American foreign policy is to miss any chance of influencing it.

The American belief that freedom is the ultimate human goal - and therefore that all men everywhere must want it - arises from a failure to understand the extent to which America as a nation is unique in its historical and philosophical roots.

The American population consists of people who are themselves, or are descended from, individuals who made a personal decision to accept the risks of freedom (with the notable exception of the African slaves, who did not enter the country of their own free will and whose descendants have had tragic difficulties in benefiting from the American dream).

Oddly enough, considering that its population is more cosmopolitan then ever, America has become even more insular over the past 30 years, to an extent that I find deeply shocking whenever I visit. Most Americans now have very little comprehension of how unlike the rest of the world they are.

They do not appreciate that their willingness to submit all their hereditary baggage - ancient tribal hatreds, extended family loyalties, religious commandments - to the rule of secular democracy is an exceptional, not a natural, condition.

But though they may have difficulty in comprehending why everyone does not want what they have - the great secret of individual self-determination and fulfilment - they do know that what they have has been bought at a price.

Giving up all the old securities of authoritarian faith, clan loyalties and homogeneous local cultures, which place such limitations on life in the old countries of the world, has created huge social unease and chronic anxiety.

The disruption and dislocation of American life makes it violent and perpetually unstable in ways that less free societies can never know.

But whatever the delusions and mistakes, the American experience has produced one important truth: the two conditions most conducive to peace and prosperity are liberal, democratic government and free-market economics.

The challenge of this century will be to extend those things to the parts of the world that do not have them.

Whatever its blunders, America is, at least, trying to do that. We would have to be deeply cynical and selfish not to support that intention.