The New Republic this week reminded us of the Clintonian optimism: "At the dawn of a new millennium, we can envision a new era that escapes the 20th century's darkest moments, fulfils its most brilliant possibilities..."

Clinton's sweet song is terminated, along with many of our illusions. Indeed, his reputation will scarcely recover, since the US national security failures so starkly exposed a fortnight ago accumulated under his watch.

That giddy post-Cold War decade of complacent prosperity, relative peace and economic globalisation has been abruptly interrupted. It is too early to assess the meaning of the September 11 attacks, yet too tempting for analysts to shun this task.

Australia's leading strategic analyst, Paul Dibb, says: "I think in many ways the current situation is more dangerous than what we saw during the Cold War. In that contest we had so-called rules of the game. Each side knew how far to go and how far not to go. There were high-level agreements and international negotiations. If the Soviet Union had planned what the terrorists did to New York and Washington, they knew there would have been American retaliation, which is why it didn't happen."

The terrorists have violated American immunity: this was the idea of the US as a safe haven, in control of its destiny and able to dictate the terms of its relations with other nations. This immunity is compromised, and probably lost forever. Americans mourn for their family and friends, but they also mourn for the violation of this unique sense of national self. It is a loss President George W. Bush confronted when he said the US had been attacked once before, one Sunday in 1941 – but never at its urban heart.

A decade ago, Americans celebrated as the Berlin Wall fell, communism collapsed and the 20th century ended in a blaze of triumph for liberal-democratic capitalism. Francis Fukuyama made the big call. This system (America's system) was "the end point of mankind's ideological evolution" and the final form of governance. It was a judgment that humankind had conquered the demons of its past on the road to a deeper enlightenment.

Now there is another roar: a roar not just from the past, but from the caves of history. The postmodern, globalised, financially interdependent multicultural world best symbolised by New York is beset by a force from the medieval world; a force that rejects the contemporary system of state-to-state relations originating with the 1648 Treaty of Westphalia, a force that defies comprehension because it embodies what has been rejected – fanaticism, absolutism, religious fundamentalism. Its language is that of martyrs – and martyrs, you may have noticed, are somewhat out of fashion in the secular West. It uses the tools of the present, but its mind-set is ancient. It is a struggle between the pre-modern and postmodern mind-sets, an entirely new and epic challenge.

The opinion pages are filled with well-meaning pieces that there should be no US retaliation or that Osama bin Laden should be brought to trial. It's a bit like sending Rumpole of the Bailey to fight Hitler. Does anybody believe this act is merely a one-off that won't be repeated? Denial is an unsurprising instinct, but the task is to address the challenge. Such sentiments overlook the words of bin Laden and his supporters. They aim to launch more attacks, kill more Americans, and overthrow governments. Doing nothing only gives them heart. Bush is correct in his effort to construct a broad-based and long-run campaign.

THE attack has seen a transformation within the US. There is a new sense of unity, a new spirit between the President and the Congress. The US now displays a capacity for national action that it has not revealed for decades, and which many people may have forgotten it still had.

The grave problem lies in the means. Bush's task is to eliminate the core terrorist network, which he says runs into 60 countries, yet avoid triggering Islamic revolutions that see new dominoes fall to enemies of the US. There is little point in reclaiming Afghanistan if the price is losing Pakistan.

Bush repudiated any suggestion of a war against Islam. Yet this is exactly the paradigm that his enemies present. They seek, and they announce, that this will be an Islamic war against the US. This week, The Economist recalled Samuel Huntington's early-1990s brutal assessment that the people of the Muslim world are "convinced of the superiority of their culture and obsessed with the inferiority of their power".

It is apparent that Bush cannot win by guns alone. The US needs not only a military response but a reassessment of its political policies across the Middle East and Central Asia. It needs to win the battle of ideas as well as the military battle.

Meanwhile, the idea seems to persist that Australia has offered an open-ended military commitment to the US. This is not the case. Australia's position has been to assist "within its capabilities". These are John Howard's words. They mean what they imply &3150; that Australia will decide its contribution after any US request. Any notion that Australia should have delayed its political support for the US would never have been entertained by any Australian government.