After any catastrophic event, we assume that things will never be the same again. Security becomes intense, political rhetoric reaches new heights.
In the first days after the World Trade Center and the Pentagon were hit, every politician and commentator seemed to think the world had indeed changed.
An extraordinarily violent, intentionally spectacular act of terrorism had been committed. A declaration of war - the 'war against terror' - followed.
A year later, the world does not seem to have changed so very much after all. The attacks on New York and Washington were not followed up.
The war against terror has not been conspicuously successful outside Afghanistan. Osama Bin Laden has not been found, and the world is waiting with a certain nervousness in case another big attack takes place.
Policy focus
At the same time, many airlines and airports have imperceptibly relaxed their security standards. You can even get steel knives with your in-flight meal again.
It isn't so much that the world has changed as that President George W Bush's distinctive policies, of putting American interests resolutely first, have had a year to develop.
The attacks of 11 September simply gave that policy a particular focus. But even without the attacks he would have pursued American political and economic aims aggressively; supported Israel in its own 'war against terror', which is how Israeli Prime Minister Ariel Sharon presents his struggle with the Palestinians; turned up the heat on Iraq and demanded the support of his friends and allies for his campaign.
In some ways the world has not changed nearly as much as it might have.
Support for Israel
After 11 September Iran showed signs of wanting to move closer to the United States politically. President Bush's 'axis of evil' speech in January 2002, linking Iran to its bitter enemy Iraq and suggesting a connection with the events of 11 September, ended that.
The war on terror gave President Bush further reasons to support Israel while condemning Yasser Arafat and the Palestinians.
Syria, which under its new President Bashar al-Assad might have shifted closer to the American line, moved further away from it. So no movement anywhere in the Middle East at all.
The political fall-out from 11 September helped a whole raft of countries which had problems with disaffected population groups, from India to Israel, China to Russia, and Indonesia to the Philippines.
No solutions
The war on terror provided them with a new vocabulary and a new justification for using harsh military methods - and the United States, obliged by its commitment to wage war on terrorism wherever it found it, has backed these and other countries in policies it would once have been much less enthusiastic about.
So 11 September has given President Bush a first-class opportunity to demonstrate America's position as the world's unchallenged superpower.
Yet, frustratingly for him, narrowing every political question down to a single one - are you for or against terrorism? - has not made any of the world's more complicated problems any easier to solve.