It is a terrible memory, says the latest opinion piece in The Economist. A memory of four plane-loads of people, setting off on a beautiful morning but then hijacked to their deaths.

A memory of thousands of innocent, unsuspecting civilians, of many nationalities, slaughtered when three planes hit the twin towers of the World Trade Centre and one side of the Pentagon; and of many more, lucky to survive but living ever since with the nightmare of that day, one year ago.

It is a memory, also, of how the world looked a moment before 8:48am on Sept. 11 2001, and of how, by the end of that day, the world was different.

A year later, much more has changed, and mostly for the better. An America that Osama bin Laden and his al-Qaeda terrorists wanted to frighten, proving that the world’s greatest power was actually weak, vulnerable and cowardly, has shown a remarkable resolve. Its patient but determined use of military power in Afghanistan, and threat of it in Iraq, has created more fears of its strength than contempt for its weakness.

Afghanistan was liberated from the Taliban, al-Qaeda’s bases and forces there were destroyed or scattered, and that war-torn country managed to choose its own provisional government. An astonishingly broad alliance backed America in that war, and the two old superpower foes—Russia and China—were respectively supportive and acquiescent.

Some of the successes lie in what has not happened rather than what has. America has not turned in on itself, seeking to hide from a hostile world: rather, its international engagement has been reinvigorated, even if its tolerance of opposition or of compromise in that engagement has diminished.

The process of globalization has not been put into reverse, either by the demands of security or by a disenchantment with open markets: if anything, the chances of a new round of trade liberalization have increased, despite a weak world economy. And, most important of all, if bin Laden and his sort hoped that their atrocities, and the American military response to them, would bring to life a mass movement in the Islamic world, they have so far been sorely disappointed. Not in Pakistan, not in Saudi Arabia, not in Egypt, not in Palestine, not in Indonesia, not even in Afghanistan itself have the numbers fighting, or even marching, against America ever gone beyond a few thousand at a time.

Moreover, there has been no big terrorist success since September 11th, although several attempts appear to have been thwarted.

That is where, for all the success, the memory becomes important again. In at least one vital respect the world has not changed in the past year. This is that the sort of extremists who carried out the slaughter on Sept. 11 could do so again. Their operations have been disrupted, their hopes may have been disappointed.

But last year’s attacks took just a handful of people, with a handful of money, using low-technology methods. The ability of police and intelligence services, in America but also elsewhere, to stop them has improved, but not to such a degree as to provide a true sense of security.

Anyone who believes the risks are small should think back to Sept. 10 last year, when the risks also looked small; and should then ask themselves whether the attitudes and perceived grievances that persuaded 19 well-educated men to kill themselves and thousands of civilians have meanwhile changed or gone away.