"They want to bring down the US not just for what it does, but for what it is"

The USA has made plain its determination to extirpate terrorism, wherever it lurks and however long it takes. So we must expect many follow-ups to Afghanistan, with various actions in the Middle East, Africa, and Asia.

Are those necessary? Yes. Waiting forlornly for terrorists to stop voluntarily will simply give time for more 11 Septembers: 80 per cent of al-Qaeda members are outside Afghanistan and 70,000 have attended training schools. Moreover, there are other terrorist organisations and other terrorist-happy states.

But shouldn’t the USA concentrate instead on removing the causes of the terrorists’desperate and self-immolating actions? No. The extreme Islamists want an end to Israel; an end to Western-leaning Muslim governments, notably in Saudi Arabia; an end to the US presence in the Middle East, indeed generally, for they want to bring down the USA not just for what it does but for what it is. These are not issues susceptible of compromise or adjustment - on either side.

Wouldn’t further US action splinter the coalition? Perhaps. But the US, with vital interests and lives at stake, and with large capabilities on its own, is not about to give others a veto.

If the arguments against further action fail, what are those in favour?

Not revenge, not justice, not punishment, but prevention: the prevention of more attacks; prevention by elimination, not by deterrence - the prospect of immolation doesn't work against those who seek self-immolation. The future, not the past, is the driver. Hoping against hope that the past will not repeat itself is to lose all hope for the future.

So what should be the next target? Iraq is the most obvious, for state-organised terrorism is more dangerous than private-enterprise, though state-tolerated, terrorism. Bin Laden had to resort to civilian weapons; Saddam has and is acquiring military weapons - weapons, moreover, of mass destruction, capable of taking out whole cities, or at least much of their populations.

The first step has already been taken: the US ultimatum to Saddam to allow back UN weapons inspectors - or else.

If he does not comply, the next step will be to use force, from the air and in his Sunni heartland, to compel his acquiescence. If that fails to change his mind, the third step must be to change the government. That cannot be done from the air alone: ground action is required, involving much more than a velitation; and a new government needs to be installed.

Iraq is not as conveniently placed as Afghanistan in these regards: neither well-armed and experienced local fighters nor organised opposition are to hand; bases will not be easy to come by; and Saddam has large forces.

Still, something could be made of the two existing Western-enforced air exclusion zones in Iraq, where (respectively) the predominant Kurds and Shias dislike Saddam and his Sunnis.

If as is likely the USA were to proceed against Iraq, should Australia again support it? Yes: for three reasons of Australian national self-interest.

First, Australia is already a potential terrorist target – see the recent Indian revelation. Indeed, some 20 in Australia are reported by a former security head to have had links with al-Qaeda - perhaps those who say they are not Australian Muslims but only Muslims living here.

Second, if Islamist terrorism were allowed to spread, Australia would also suffer because the world would become a very much worse-off place.

Third, the USA would be much diminished, and with it Australia's future.

For September 11 shewed the USA with less physical safety than was once thought, and without the means of deterrence. With this vulnerability, the fear of US power, and the prospects for its economy, have been diminished. If the USA is judged less able to prevent further Islamist attacks, or if action against Iraq were to fall short, the USA would be even further diminished.

That the USA should not have its "strength by limping sway disabled", should not lose its confident and on the whole benign and beneficent leading place in the world, is a prime Australian national interest. To help in whatever way we appropriately can is our duty - not to the USA, for we owe it none - but to ourselves.

Des Moore is director of the Institute for Private Enterprise and on the Australian Strategic Policy Institute board. The views are his.