Understanding the past, Felipe Fernández-Armesto asserted in Truth: A History, is akin to “a nymph glimpsed bathing between leaves; the more you shift perspective, the more is revealed. If you want to see the whole you have to dodge and slip between the different viewpoints”.

That perspectives on September 11, 2001, have already altered in five years is undeniable. In the immediate aftermath of the day itself, America was viewed, all but universally, as the victim of an atrocity. Apart from Islamist fundamentalists and the far left fringe, few saw any difficulty in apportioning blame or awarding moral status. While this vast consensus frayed when George W. Bush ordered that the Taleban be chased out of Afghanistan and ejected al-Qaeda from their base, most people regarded this response as rational. The first anniversary of September 11, 2001, was thus, generally, an occasion for unity.

This will not, alas, be the same today. In the United States and, especially, elsewhere, the respects paid to the dead will take place alongside rancour among the living. It has become almost acceptable, even fashionable, to allow outrageous conspiracy theories an airing that simple decency should deny. Less bizarrely, but no more accurately, it is claimed that those who lost their lives on 9/11 were cynically exploited by an Administration that had ached to depose Saddam Hussein in Iraq and suddenly discovered that circumstances had offered the pretext required.

The argument is understandable yet unduly simple. It begins with a string of events triggered just before 9am in New York City five years ago, moves on through Afghanistan and then on to Iraq and the controversy that has come with that mission. But 9/11 was not the beginning. It was not the opening shot of a terrorist campaign, it was just the loudest. There had been other attacks or attempted assaults, directed by Osama bin Laden and his acolytes and stretching back the better part of a decade. It is a campaign rooted in a desire to recapture a lost Islamic world, not a forensic and bloody assessment of recent American foreign policy.

Yet the sheer drama of what took place five years ago has blinded people to the history that lies before September 11, 2001, and produced an excessive focus of the history that came after. It is like looking at the flowers of a plant while disregarding its roots. The actual account of what has brought contemporary terror about can be found in the expulsion of Muslims from Spain in the 15th century (a deed done before Columbus set sail for the Americas) or, at the latest, a defeat outside the gates of Vienna 200 years after.

That a creed can combine a vision of the caliphate centuries old while employing the internet and satellite telephones to advance its ambitions will strike most Americans and Europeans as incredible. Even so, that was and is the essence of the September 11 story. To ignore this, and place the blame on Israel-Palestine, Afghanistan and Iraq is to misunderstand the creature that is al-Qaeda. It is the product of a very long history.

None of this is to excuse or to excise tragic mistakes that have been made in the past five years. America’s aims and ideals have been noble, but they have often been poorly articulated, and the execution of policy, particularly in Iraq, has been shamefully inept at times, at a huge cost to the reputation of the United States and its capacity to pursue worthy goals in the global arena. It is right to ask searching questions of the strategies and tactics selected, and to demand change where necessary. But it is wrong to conclude that this is what September 11, 2001, is all about.

It is also too convenient. It allows us to avoid core issues that are uncomfortable to contemplate. How liberal can liberal societies afford to be? How “multi” a multiculturalism is wise? Is a clash of civilisations emerging? Beside this, the timing of US troop withdrawals from Iraq is virtually immaterial. In truth, we are still glimpsing September 11, 2001, from between the leaves.