September 11 has given to us a planet we barely recognise. In a sense it revealed what was already there, largely unremarked, since the collapse of the Soviet Union: the unprecedented preponderance of a single power. It also revealed the longstanding but increasingly dynamic loathing of this power in the Islamic world, where anti-Zionism and anti-semitism are exacerbated by America's relationship with Israel - a relationship that many in the west, this writer included, find unnatural. In addition, like all "acts of terrorism" (easily and unsubjectively defined as organised violence against civilians), September 11 was an attack on morality: we felt a general deficit. Who, on September 10, was expecting by Christmastime to be reading unscandalised editorials in the Herald Tribune about the pros and cons of using torture on captured "enemy combatants"? Who expected Britain to renounce the doctrine of nuclear no-first-use? Terrorism undermines morality. Then, too, it undermines reason.

Osama bin Laden is an identifiable human type, but on an unidentifiable scale. He is an enormous stirrer - a titanic mixer. Look how he's shaken us up, both in the heart and in the head. One could say, countervailingly, that on September 11 America was visited by something very alien and unbelievably radical. A completely new kind of enemy for whom death is not death - and for whom life is not life, either, but illusion, a staging-post, merely "the thing which is called World". No, you wouldn't expect such a massive world-historical jolt, which will reverberate for centuries, to be effortlessly absorbed. But the suspicion remains that America is not behaving rationally - that America is behaving like someone still in shock.

The notion of the "axis of evil" has an interesting provenance. In early drafts of the President's speech the "axis of evil" was the "axis of hatred", "axis" having been settled on for its associations with the enemy in the second world war. The "axis of hatred" at this point consisted of only two countries, Iran and Iraq. whereas of course the original axis consisted of three (Germany, Italy, Japan). It was additionally noticed that Iran and Iraq, while not both Arab, were both Muslim. So they brought in North Korea.

We may notice, in this embarras of the inapposite, that the Axis was an alliance, whereas Iran and Iraq are blood-bespattered enemies, and the zombie nation of North Korea is, in truth, so mortally ashamed of itself that it can hardly bear to show its face. Still, "axis of hatred" it was going to be, until the tide turned towards "axis of evil". "Axis of evil" echoed Reagan's "evil empire". It was more alliterative. It was also, according to President Bush, "more theological".

This is a vital question. Why, in our current delirium of faith and fear, would Bush want things to become more theological rather than less theological? The answer is clear enough, in human terms: to put it crudely, it makes him feel easier about being intellectually null. He wants geopolitics to be less about intellect and more about gut-instincts and beliefs - because he knows he's got them. One thinks here of Bob Woodward's serialised anecdote: asked by Woodward about North Korea, Bush jerked forward saying, "I loathe Kim Jong II!" Bush went on to say that the execration sprang from his instincts, adding, apparently in surprised gratification, that it might be to do with his religion. Whatever else happens, we can infallibly expect Bush to get more religious: more theological.

When the somnambulistic figure of Kim Jong II subsequently threw down his nuclear gauntlet, the "axis of evil" catchphrase or notion or policy seemed in ruins, because North Korea turned out to be much nearer to acquiring the defining WMDs, deliverable, nuclear devices, than Iraq (and the same is true of Iran). But it was explained that the North Korean matter was a diplomatic inconvenience, while Iraq's non-disarmament remained a "crisis". The reason was strategic: even without WMDs, North Korea could inflict a million casualties on its southern neighbour and raze Seoul. Iraq couldn't manage anything on this scale, so you could attack it. North Korea could, so you couldn't. The imponderables of the proliferation age were becoming ponderable. Once a nation has done the risky and nauseous work of acquisition, it becomes unattackable. A single untested nuclear weapon may be a liability. But five or six constitute a deterrent.

From this it crucially follows that we are going to war with Iraq because it doesn't have weapons of mass destruction. Or not many. The surest way by far of finding out what Iraq has is to attack it. Then at last we will have Saddam's full cooperation in our weapons inspection, because everything we know about him suggests that he will use them all. The Pentagon must be more or less convinced that Saddam's WMDs are under a certain critical number. Otherwise it couldn't attack him.

All US presidents - and all US presidential candidates - have to be religious or have to pretend to be religious. More specifically, they have to subscribe to "born again" Christianity. Bush, with his semi-compulsory prayer-breakfasts and so on, isn't pretending to be religious: "the loving God behind all life and all of history"; "the Almighty's gift of freedom to the world." "My acceptance of Christ", Bush has said (this is code for the born-again experience of personal revelation), - "that's an integral part of my life." And of ours, too, in the New American Century.

One of the exhibits at the Umm Al-Maarik Mosque in central Baghdad is a copy of the Koran written in Saddam Hussein's own blood (he donated 24 litres over three years). Yet this is merely the most spectacular of Saddam's periodic sops to the mullahs. He is, in reality, a career-long secularist - indeed an "infidel", according to Bin Laden. Although there is no Bible on Capitol Hill written in the blood of George Bush, we are obliged to accept the fact that Bush is more religious than Saddam: of the two presidents, he is, in this respect, the more psychologically primitive. We hear about the successful "Texanisation" of the Republican party. And doesn't Texas sometimes seem to resemble a country like Saudi Arabia, with its great heat, its oil wealth, its brimming houses of worship, and its weekly executions?

The present administration's embrace of the religious right also leads, by a bizarre route, to the further strengthening of the Israel lobby. Unbelievably, born-again doctrine insists that Israel must be blindly supported, not because it is the only semi-democracy in that crescent, but because it is due to host the second coming. Armageddon is scheduled to take place near the hill of Megiddo (where, in recent months; an Israeli bus was suicide-bombed by another kind of believer). The Rapture, the Tribulation, the Binding of the Antichrist: it isn't altogether clear how much of this rubbish Bush swallows (though Reagan swallowed it whole). VS Naipaul has described the religious impulse as the inability "to contemplate man as man", responsible to himself and uncosseted by a higher power. We may consider this a weakness; Bush, dangerously, considers it a strength.

Even a cursory examination of Saddam's character suggests that he will never fully disarm, any more than he would choose to revisit his childhood and walk shoeless and half-naked through the streets of Tikrit. He started as he meant to go on when, in 1991, he appointed his younger (and less feral) son Qusay to the chairmanship of the Concealment Operations Committee. The assault on Iraq is expected to cost America 0.5 per cent of its GDP; Saddam's wars, and the subsequent sanctions, have cost Iraq about 20 years of GDP, according to The Economist. Such are his priorities. It has been in Saddam's power to alleviate the immiseration of his people. Instead a pattern of paranoia, gangsterism and chronic kleptomania, has established itself.

It is important to remember that Saddam, despite his liking for medals and camouflage outfits (and for personally mismanaging his armies), was never a military man. He came up through the torture corps in the 1960s, establishing the Baath secret police, Jihaz Haneen (the "instrument of yearning"), and putting himself about in the Qasr al-Nihayah ("the Palace of the End"), perhaps the most feared destination in Iraq until its demolition, after an attempted coup by the chief inquisitor, Nadhim Kazzar, in 1973.

Saddam's hands-on years in the dungeons distinguish him from the other great dictators of the 20th century, none of whom had much taste for "the wet stuff". The mores of his regime have been shaped by this taste for the wet stuff - by a fascinated negative intimacy with the human body, and a connoisseurship of human pain. One is struck, too, by how routinely Saddam's organs have used familial love as an additional instrument of torture. Here, in moral terms, we decisively enter the palace of the end, as the interrogator consigns your child to a sack full of starving cats.

I said earlier that America's war aims remain partly undisclosed. The frank answer to the question "why now?", for instance, would be the usual jumble, something like: a) to pre-empt Saddam's acquisition of more WMDs; b) in good time for the next election; and c) before the weather gets too hot. Without his war, Bush is an obvious one-term blowhard; and he listens to his political handler, Karl Rove, at least as keenly as he listens to Donald Rumsfeld. The supplementary motivation, hatched at the thinktank and prayer-breakfast level, is, I fear, visionary in tendency. It has been noticed that a great deal of the world's wealth is in the hands of a collection of corrupt, benighted and above all defenceless regimes. The war, as they see it, will not be an oil-grab so much as a natural ramification of pure power: manifest destiny made manifest, for the good of all.

Tony Blair must have known that war was inevitable more than a year ago, when Bush started talking, with vulgar levity, of "taking Saddam out". In the past Blair has been consistently tough on the Iraq question, just as France has been consistently, and venally, lenient (as early as the mid-1970s Jacques Chirac was known as "Monsieur Iraq"). More generally, perhaps, he feels that British interests are better served by continuing to ride on the American elephant, even as it trumpets its emancipation from the influence of Europe; and that the total isolation of Washington would only heat Bush's internal brew of insecurity and messianism.

There are two rules of war that have not yet been invalidated by the new world order. The first rule is that the belligerent nation must be fairly sure that its actions will make things better; the second rule is that the belligerent nation must be more or less certain that its actions won't make things worse. America could perhaps claim to be satisfying the first rule (while admitting that the improvement may be only local and short term). It cannot begin to satisfy the second.

We contemplate a kaleidoscope of terrible eventualities: a WMD attack on Israel, and a WMD response (conceivably nuclear); civil war in Iraq. and elsewhere, together with all manner of humanitarian disasters; fundamentalist revolutions in Egypt and Jordan; and, ineluctably, an additional generation of terror from militant Islam. Meanwhile, common sense calmly states that an expanded version of the present arrangement (inspectors, monitors, full exposure to world opinion) is sufficient to contain and emasculate Saddam until pressure builds for a coup; and that the "war on terror" can start only with the dismantling of the settlements in the territories occupied by Israel.

But the necessary momentum has already been achieved, and the first humanitarian disaster will of course be the war itself.

"O people of Iraq... By God, I shall strip you like bark, I shall truss you like a bundle of twigs, I shall beat you like stray camels... By God, what I promise, I fulfil; what I purpose, I accomplish; what I measure, I cut off." You could imagine Saddam Hussein muttering these words when he assumed the presidency in 1979. It is with weariness and shame that we hear them from our own leaders, in various encryptions - echoing al-Hadjadj, the newly arrived governor of Iraq, in the year 694. And what he measured, he cut off.