The US has gained an understanding of the costs of war for which its European allies have hitherto wished in vain, says Amity Shlaes.

Shortly after the attack on Pearl Harbor, Metro-Goldwyn-Mayer produced an earnest film aiming to show what courage on the home front was all about.

The studio chose England in the summer of 1939 as setting for its film, the opening scenes of which portray a politically oblivious English matron, the sort of caricature who heads into town on the morning train to pick up an expensive hat, and then conceals her feathery extravagance from her spouse. But soon comes September, and war. The droning of enemy planes low overhead alters everything. And this same housewife, Mrs Miniver, rises to the occasion, stewarding her family through the Battle of Britain.

With her support, her son leaps to join the Royal Air Force. Her husband pilots the family boat down the Thames to help the navy. She herself handily disarms a Luftwaffe pilot who turns up among her garden geraniums.

Mrs Miniver inspired Britons - Winston Churchill, the prime minister, called it "more powerful to the war effort than the combined work of six military divisions." But it was the American reception that proved spectacular. Americans flocked to cinemas to study the heroism of the English rose, making the film more popular than any of that decade bar Gone with the Wind. Part of the US fascination stemmed from self-doubt. Lacking their own experience of home-front valour, Americans wondered: could they too, if necessary, rise to the occasion?

And so they continued to wonder, for a full six decades. For postwar America, the America of the period that ended so abruptly on September 11, was something of paradox - a superpower, a strong fighter, but also a self-conscious naif, not tested on its home turf.

In the early part of the cold war, of course, there were still many Americans - soldiers and former soldiers - who knew war abroad. But in recent decades and with the end of the draft, that knowledge has receded, turning the US into the equivalent of a nation of oblivious hat-buyers. Americans never dreamed that their nation would create, as President George W. Bush did last Thursday, a powerful Office of Homeland Security. This circumstance shaped US behaviour abroad.

Americans were aware of their missing experience and sought to compensate for it, however artificially. To inform themselves about the Soviet Union and Europe, successive administrations hired European-born experts such as Henry Kissinger and Zbigniew Brzezinski - people who had personal experience of the threat at hand. Citizens travelled as tourists to divided Berlin to peer from Checkpoint Point Charlie into that unknowable - communism.

But especially after Vietnam and as the cold war faded, it was difficult for the US to convince itself it truly confronted risk of attack. And if America could never be hurt, what did "elsewhere" matter? US officials might mouth the old line, but the will to act or plan was gone.

This cavalier mood was especially prevalent in the mid- and late-1990s, the period in which Hollywood gave us another war film, as cynical as Mrs Miniver was earnest. Wag the Dog was the story of a poll-obsessed White House that manufactured a mini-war to increase its political standing. Although the film exaggerated, it accurately conveyed the US conviction that "abroad" was becoming something unreal, even fictional. Short strikes from high over Iraq or Yugoslavia might be all right, but was it really worth undertaking projects that might disturb a night's sleep at home? It was even hard to write consistent policy.

This attitude disillusioned America's allies and European citizens. If the US had declared itself to be opposed to terrorism, why did the White House not take London's side when it came to the Irish Republican Army? If the US stood for freedom, why did it not move to topple Slobodan Milosevic earlier? The Allies might be right or wrong on such specific issues. But they were certainly correct in their perception that America did not always acknowledge the stakes of the game it played.

The most sinister thing about US inconsistency was that it caused America to be misread by its enemies. It is said that Somalia, where the US engaged and then fled after the death of 18 soldiers in Mogadishu, convinced Osama bin Laden that Washington would do anything to avoid the sight of body bags.

This may have been true, on some occasions, of body bags containing professional soldiers killed in far-off places. What bin Laden failed to understand was that body bags containing New York's neighbourhood firefighters killed at home would produce quite another reaction.

In other words, if anything positive can be said to have come of the September 11 suicide bombings, it is that they have given the US something of the understanding of war that Europeans have always wished it might have. America too has now been tested, and has discovered in herself a Miniver-scale resolve. Both US citizens and the government are now proceeding more confidently. This is what Mr Bush meant when he said on Thursday that "we have found our mission and our moment".

The change may not bring the sort of formalised multilateralism European leaders hanker after, but it has given new life to the US side of the old special relationship with Britain. Prime ministers have always been welcome in the US, but none since Churchill has been so appreciated as Tony Blair was when he appeared in the gallery to watch Mr Bush outline his war plans.

For New York and Washington, unlike London, never knew until 14 days ago what it was like to wake in the night to the sound of planes overhead and to wonder, for a moment, whether those planes were "theirs" or "ours". And now they do.

© Copyright 2001 Financial Times