Paul Kennedy's notion of "imperial overstretch" in his The Rise and Fall of Great Powers was a more sophisticated contribution to the literature of decline. In fact, the current crisis in the US "empire" came not as a result of overstretch but of retrenchment. Still, the book sold and sold. Titles are important, because we crave simple answers to big and frightening questions. Will we be rich for ever? Will there be another war? Will the world come to an end? For it to work in media-saturated America, the title has to be simple and dramatic enough for talk-show hosts to handle with ease. People must be able to speak with absolute authority on the main idea without ever having read the book. This makes it rather harder for good ideas to take off, for good ideas are by definition complicating, qualifying, sceptical, and thus, on the whole, not terribly sexy.

Samuel P Huntington's The Clash of Civilisations - enjoying fresh popularity since September 11 - is by a long chalk the most successful bad idea of our time. One reason for its fame is that so many intellectuals have felt the urge to attack it. Few ideas have enjoyed such bad publicity. But as Oscar Wilde, who had a surprising number of rather good ideas, told us, enough bad publicity becomes good publicity. Huntington's notion that future wars will be fought between civilisations, not nation-states, may be wrong, but it is not stupid. The merit of a clever bad idea is that it provokes thought, if only to contradict it.

Still it is a bad idea. First of all, Huntington is fuzzy about what constitutes a civilisation. He talks about civilisational "faultlines", along which wars will be, or already are being, fought. He talks about differences between civilisations that "are not only real, but basic". And these basically different civilisations are western, Latin-American, Confucian, Islamic, Hindu, Slavic-Orthodox, African, and Japanese. Most of these basic differences appear to be religious. But if by western he means Christian, why then is Italy, say, basically different from Chile? And in what way is Confucian Japan basically different from Confucian China or Korea? And if the "faultlines" dictate our loyalties, why did the west (too late, to be sure) decide to take sides with the Bosnian Muslims against the Serbs? Surely not because Clinton and Blair are Christians. And what is the common civilisation of Africa?

Even in some of the worst ideas, there can be a nugget of truth. Huntington's claim that fundamentalist religion is replacing allegiance to nation-states may not be generally true, but clearly is in the case of Osama bin Laden and his followers. But we don't wish to stop him in the name of Christendom, or western values, but because suicide bombers are mass murderers.

The most serious flaw in Huntington's thesis is the lack of politics. All kinds of more or less murderous dictators, crusaders (I choose the word carefully), and their intellectual apologists, claim to be acting as defenders of the faith, or of a particular civilisation. Maoism, despite its lip service to an international creed, was a brutal attempt to reclaim Chinese civilisation. In the Middle East, dictators, as well as religious extremists, claim to act as guardians of the Islamic faith.