It stands to reason 19 men cannot change history. But they did. Five years and two U.S.-led wars later, the world created by the Sept. 11th hijackers is a darker place than almost anyone predicted at the start of the new century. Al-Qa'ida itself might have been battered and dispersed, but the idea it stands for has spread its poison far and wide.
The essence of that idea, so far as a coherent one can be distilled from the ferment of broadcasts and fatwas issued by Osama bin Laden and his disciples, is that Islam is everywhere under attack by the infidel and that every Muslim has a duty to wage holy war, jihad, in its defence.
The United States is deemed a special target for having trespassed on the Arab heartland. Intoxicated by their defeat of the Soviet Union in Afghanistan in the 1980s, the jihadists are hungry to topple another superpower.
This cause had deadly adherents before the attacks on the Pentagon and the World Trade Centre in 2001. Bin Laden issued his Declaration of the World Islamic Front for Jihad against the Jews and Crusaders in 1998, the year Al-Qa'ida bombed two U.S. embassies in East Africa.
But an honest tally of the record since Sept. 11 has to conclude the number of jihadists and their sympathizers has probably multiplied many times since then. It has multiplied, moreover, partly as a result of the way the U.S. responded.
The first of the two wars George W. Bush launched after Sept. 11 looked initially like a success, and compared with the second, it still is. Al-Qa'ida operated openly in Afghanistan and enjoyed the protection of its noxious Taliban regime, which refused the United States' request to hand bin Laden over. The U.S. invasion, one month after the United States itself had been attacked, therefore enjoyed broad international support.
The fighting ended swiftly and the political aftermath went as well as could be expected in a polity as tangled as Afghanistan's. By 2004, a first-ever free election had legitimated the presidency of Hamid Karzai. A ramshackle but representative parliament took office in 2005.
The country is plagued by warlordism and the opium trade, and Taliban fighters are mounting a challenge in the south. But they do not yet look capable of dislodging the new government in Kabul.
Even though bin Laden himself eluded U.S. forces in Afghanistan, the invasion deprived Al-Qa'ida of a haven for planning and training. This achievement, however, was cancelled out by the consequences of Bush's second war: the invasion of Iraq in March 2003.
There, 31/2 years later, fighting and terrorism kill hundreds every month, providing the jihadists with both a banner around which to recruit and a live arena in which to sharpen their military skills.
Had Iraq turned out better, fewer people would have continued to complain that this war, unlike Afghanistan's, was conceived in sin. Loathsome though he was, Saddam Hussein had no link to Al-Qa'ida or the Sept. 11 plot. Moreover, the prewar claims of the United States and Britain that he had defied the Security Council by keeping his banned chemical and biological weapons, and continuing to seek nuclear ones, turned out to be false.
In the battle for world opinion, this mistake, if such it was, had calamitous consequences.
Opinion polls show millions of Muslims now think the United States' real aim in Iraq was to grab its oil, help Israel, or, just as bin Laden said all along, wage war on Islam.
Bush and British PM Tony Blair tried and failed to win a clear United Nations mandate for war. By invading without one, they made themselves vulnerable to the charge the war was unlawful.
The quarrel in the Security Council widened a rift between the U.S. and Britain on one hand and France, Germany and Russia on the other. But this would have counted for much less if the weapons of mass destruction had existed. When it transpired that they did not, Muslims - and many others - began to assume they had been just a pretext.
There were those who supported the Iraq war solely because of the danger that a Saddam Hussein with a biological or atomic bomb would, indeed, have posed. But Bush and Blair refused after the war to be embarrassed by the absence of the weapons that had so alarmed them beforehand. They stressed instead all the other reasons why it had been a good idea to overthrow Hussein.
In Los Angeles last month, Blair argued the invasion was all about supporting Islam's moderates against its reactionaries and bolstering democracy against dictatorship.
Such arguments no longer sell in the West, let alone the Muslim world. If it was all about dictatorship, what about the dictatorship the West continues to embrace in Saudi Arabia, and the quasi-dictatorship in Pakistan? If it was about helping Islam's moderates against its reactionaries, what is so clever about stepping in to someone else's civil war?
Besides, the horrors of pre-invasion Iraq had nothing to do with Islam's inner demons. Hussein's was a secular dictatorship in which Islamists of all stripes kept their heads down.
It is true, and it is commendable, that once the U.S. and Britain had toppled Hussein, they helped to organize free elections. They are right to support Iraq's new government and to make the argument for democracy elsewhere in the Arab world.
But portraying the whole enterprise as if it had from the start been all about an experiment in democracy just makes Muslims crosser. By what right do you invade someone else's country in order to impose a pattern of government?
Whatever else it might become, Iraq has so far been an own-goal in the battle for hearts and minds - and not just Muslim minds. The West rallied behind the United States five years ago. Now it is split: poll after poll shows deep distrust among traditional U.S. allies, distrust that makes cooperation on everything from nuclear proliferation to trade far harder.
Some of this can be put down to the usual anti-Americanism, and the European politicians who have pandered to it. But Bush has played, unerringly, straight into anti-Americans' hands.
One vast mistake has been his neglect of Blair's advice to push seriously for the creation of a Palestinian state, instead of just saying this was his "vision." But worse has been his administration's wanton disregard for civil liberties.
Some curtailing of freedoms was inevitable. Yet Abu Ghraib, Guantanamo, the torture memos and extraordinary rendition have not just been un-American and morally wrong but also hugely counterproductive. In a battle that is largely about ideas, the U.S. seems to many to have abandoned the moral high ground and so won more recruits for the jihadists.
Still, not everything has gone Al-Qa'ida's way, either. For if, as that ferment of fatwas suggests, bin Laden's longer-term aim was to topple the pro-U.S. regimes in the Muslim world, and so establish a new caliphate, he has failed.
Of the 19 hijackers, 15 were Saudis, as is bin Laden himself. Before 2003, Al-Qa'ida had not attacked the Saudi regime. However, in May of that year, just after the United States invaded Iraq, the organization launched an offensive at home.
Suicide bombers attacked a housing compound in Riyadh, starting a campaign of terrorist violence that has claimed 200 lives. Yet the regime is still standing, and so far as anyone can tell the violence has served mainly to strengthen it.
Another prize to have eluded Al-Qa'ida is Pakistan. Like Saudi Arabia, this is a country where Islam is central to the state's idea of itself. It is undoubtedly unstable. Pakistan teems with Al-Qa'ida sympathizers and other jihadists training for operations in Kashmir and beyond. Bin Laden himself is probably hiding there.
Nonetheless, all of Al-Qa'ida's efforts to kill President Pervez Musharraf, or to deflect Pakistan from a U.S. alliance that has grown steadily closer since Sept. 11, have so far come to naught.
As in the 1990s, when jihadists mounted a violent challenge to the authoritarian states of the Muslim world, they have been defeated. This is not only because such states possess strong instruments of repression. It is also because the jihadists' grandiose aims and gruesome methods have prevented them from turning a resentment of the United States into an appetite for revolution at home.
It has not escaped the notice of Iraq's neighbours that most of the victims of Al-Qa'ida there have been fellow Muslims. Jihad in the abstract, or far away, might be all very well. But attacks inside countries such as Indonesia, Turkey and Jordan, where the victims were mainly Muslim, have turned local people away from Al-Qa'ida's cause.
If anything, that cause might have fared better in the West itself, among those whose identity as Muslims has come to take precedence over loyalty to the host country.
On July 7 last year, four very ordinary British-born Muslims blew themselves up on the London underground, leaving behind martyrdom tapes making it clear in homely Yorkshire accents that they saw "our people" as being at war with "your people."
British police claimed last month to have thwarted a more elaborate plot, also by British Muslims, to destroy up to 10 transatlantic airliners. In June, police in Toronto arrested a dozen Canadian Muslims for planning attacks, including, it is said, a plan to seize and behead the prime minister.
To many susceptible Muslims the message that the faith is everywhere under attack is evidently compelling. Jihadists are skilled at weaving the "resistance" in Palestine, Lebanon, Kashmir, Chechnya, Iraq and Afghanistan into a single narrative of persecution by the infidel.
Of the 15 million to 18 million Muslims who live in Europe (excluding Turkey), the percentage who sympathize with the bombers is small. But the hijackers proved in the U.S., and the train bombers of March 2004 in Madrid, that small numbers of terrorists can produce devastating results - and a few per cent of 15 million is still a big number.
To the secular mind, the jihadists' notion that the faith is everywhere under attack looks absurd. How can conflicts as different as those in Palestine, the Caucasus, Kashmir and the Balkans, even East Timor, be interpreted as parts of a seamless conspiracy against Islam? In Kosovo, for goodness sake, NATO intervened to protect Muslims from Christians, not the other way around.
And yet a troubling recent development is the emergence in the United States of an equal and opposite distortion. This is the idea that it is the West and its values that are everywhere under attack, and everywhere by the same seamless front of what Bush has taken to calling "Islamic fascism," as if this conflict is akin to the Second World War or the Cold War against communism.
"We are in the early stages of what I would describe as the Third World War," Newt Gingrich, a former speaker of the House of Representatives, said in July.
Al-Qa'ida did not invent terrorism. In its Baader-Meinhof or Shining Path or Irish or Basque or Palestinian guise, terrorism was the background noise of the second half of the 20th century.
But Sept. 11 seemed to portend something new. There was something different in the sheer epic malevolence of the thing: more than 3,000 dead, with destruction sliding out of a clear blue sky, all captured on live TV.
Most previous terror organizations had negotiable demands and, therefore, exercised a measure of restraint. Al-Qa'ida's fantastic aims - sweeping away regimes, reversing history and restoring the caliphate - are married to an appetite for killing that knows no limits. It boasts openly that it is seeking nuclear weapons.
Mass terrorism by Islamist extremists remains a danger. To say that the United States' mistakes have increased the threat is not to say that the U.S. caused it. It is important to remember who attacked whom five years ago. Islam had its deadly and inchoate grievances before the Iraq war and before Sept. 11.
The world must still strive to destroy Al-Qa'ida and, even more, the idea it represents. But it had better do so with cleverer means than those Bush has used so far.