When the dust clears, we will remember this week as a tragedy, not a turning point in history Â

The world has changed. Nothing will be the same again. After the enormity and the horror of what happened on 11 September 2001, such an intimation of a turning point in history, part expression of resolve, part prediction, runs like a linking thread through the responses around the world. It is a common theme of the reaction of millions of Americans to what they see as a personal affront.

The world has changed. Nothing will be the same again. After the enormity and the horror of what happened on 11 September 2001, such an intimation of a turning point in history, part expression of resolve, part prediction, runs like a linking thread through the responses around the world. It is a common theme of the reaction of millions of Americans to what they see as a personal affront.

It was a theme which recurred in yesterday's debate in the House of Commons. Jack Straw, the Foreign Secretary, declared the attacks have "changed the world" in a speech which ranged surprisingly widely in its historical references, from the error of appeasement in the 1930s to Pearl Harbor.

Is it really true? While it is obviously true for the families of the victims, in numbers unprecedented in the history of terrorism, there are reasons to be sceptical about the lasting impact of this atrocity on the rest of us. As was said more than once in yesterday's Commons debate, the intensity of the suffering of each family is unrelated to the numbers of others who find themselves in the same awful position. It is for the rest of us that the scale of the casualties seems to require that life should never be the same again.

That is, as the great dramatists have often observed, sadly not how human nature works.

Among the many historical parallels, Timothy Garton Ash, writing in these pages earlier this week, raised the analogy of the assassination of John F Kennedy. That was an event which tore at the emotions of the world, and yet which had little discernible effect on the course of history. Mr Garton Ash rejected the analogy, preferring to compare the World Trade Centre attack with the epoch-making fall of the Berlin Wall. The passage of time may lend a different emphasis. The carnage in New York undoubtedly struck millions, perhaps billions, of people around the world at the deepest emotional level. The images, as of the endlessly-repeated footage of Jackie Kennedy reaching across the car for her dying husband, have been imprinted on the world's collective consciousness.

Acts of War

This is not, however, equivalent to the end of communism or, as Mr Straw pointed out, to the attack on Hawaii which brought America into the Second World War. The assault on Pearl Harbor had a simple objective, to weaken US military power in the Pacific, striking first in a war which Japan had already decided to wage. For all the assertions that the attacks on New York and Washington were "acts of war", they are not comparable. The purpose of Tuesday's attacks was primarily the fear and shock of the attacks themselves – the object of terrorism being to induce terror. Iain Duncan Smith, the new Conservative leader, was therefore mistaken – although we know what he meant – when he declared that "such cowardly acts of evil will never succeed". They already have. All we can do is try to avoid what might be a secondary objective of the suicide hijackers, namely to provoke an overreaction by the US which might in turn help to persuade more alienated Muslims in the Middle East that the US really is an evil, anti-Muslim empire.

The attacks might change our attitudes towards tall buildings and air travel, two achievements of our technological age which are astonishingly safe and yet so vulnerable to determined and suicidal terrorists. But for how long? People's working and travelling patterns are unlikely to change much for long. Skyscrapers will still be built: the threat comes not from the design of the buildings so much as from hijacked aircraft. It must be possible to tighten aeroplane security sufficiently to make such hijackings extremely difficult. Air travel, especially within the US, will become a slightly more cumbersome, security-conscious business, as it did for a while after the fashion for hijackings in the 1970s. Will the attacks leave a more lasting impression on our societies than the IRA terror campaign did on mainland Britain before 1996 – the main legacy of which is a shortage of litter bins in central London?

Let us hope so. The main lasting change which should come about is that some of the more speculative scenarios which have often been painted have to be taken more seriously. The determined and diabolically-imaginative terrorist will always get through, in the sense that new ways will be found to kill, destroy and terrify. The historical analogy which counts – apart from Guernica in the Spanish Civil War, the first aerial bombardment of a civilian target – is the sarin gas attack on the Tokyo subway in 1995. When the Prime Minister warned yesterday of the dangers of chemical, biological and nuclear weapons, these were not simply words.

In that sense, George Bush's son of Star Wars initiative shows a sound grasp of the gravity of the threat; the objections to the plan have always been primarily practical: that it is hugely expensive, unlikely to work and a dangerous distraction from the more urgent priority of intelligence efforts to assess possible threats.

New priorities

For the associated lasting effect of Tuesday ought to be the learning of the lesson of the failure of US and allied intelligence. It is apparent now that the security services of Western democracies have failed terribly to adjust to the new priorities of the post-Cold War world. The security services seem to share our popular ignorance of the belief systems of radical Islamists. As Peter Mandelson strikingly put it yesterday, "the James Bonds of the future are not going to be found in the Travellers' Club, in The Athenaeum, they are going to be found on the streets of Bradford and Marseilles".

Understanding the grievances of the disaffected Muslim populations of the Middle East is a valuable aim in itself. Any response to the shock of four days ago which is tough on terrorism ought to be tough on the causes of terrorism too, as Fergal Keane observes (right). But even if Afghanistan and Iraq became liberal democracies overnight and the Israelis signed a new peace deal with the Palestinians, there would still be small groups of people around the world motivated by irrational ideologies and bent on destruction.

The threat of global terrorism is not perhaps as awful a threat as that of the mutual nuclear annihilation which hung over the Cold War, but it is one which will colour at least the opening decade of the new century.