n early 1979 the authoritarian and much-disliked regime of the Shah of Iran collapsed, to the rejoicing of left-wing groups everywhere in the West. Quite by chance, I was to dine in those same days in Princeton with the renowned historians Fritz Stern and John Elliott, plus one other scholar. The fourth dining partner arrived late, apologetic and a little rueful. He had given a radio interview earlier in the day, warning that the shah's overthrow by Muslim clerics would lead not to social improvement and democracy but to theocracy, intolerance and clerically controlled mayhem.

This was not a popular opinion. A fellow professor, distinguished in the field of international law but knowing little of Iran, deplored such conservatism and pessimism. And many Princeton students were outraged, since they were sure that the Iranian people, freed from the shah's yoke, would join the modern, anticapitalist, freethinking world. The gloomy, skeptical scholar was surely mistaken, and should feel ashamed of himself. No wonder he was a little rueful.

The fourth dining partner that evening was the distinguished historian of the Islamic, Arabic and Middle Eastern worlds Bernard Lewis, for many years the Cleveland E. Dodge professor of Near Eastern Studies at Princeton. As it happened, the radical, protesting students were quite wrong, and the individual and maligned scholar was completely right. He actually knew what he was talking about, because he had been studying the Muslim world -- its history, literature, culture -- for over 30 years. He had some claim to offer an opinion that deserved respect. There is a lesson here.

The same authority is still going strong. A couple of years ago he published a wonderful collection of occasional pieces, named (appropriately enough) ''A Middle East Mosaic,'' which offered numerous vignettes of a region both fascinating and disturbing. Now he has produced what may be his most significant work for a contemporary audience. ''What Went Wrong?'' is a concise study of the Muslim world's responses to the West and of its own long, sad decline.

It was completed, one must emphasize, some time before Sept. 11. Scholars of international and Middle Eastern affairs like Lewis did not need Osama bin Laden's attacks, the subsequent war against the Taliban and revelations of our shaky, ambivalent friendships with Pakistan or Saudi Arabia and other Arab states to recognize that things were out of joint between the West and much of the Muslim world. What the events of the past few months did was to call this enormous problem to the attention of a far wider audience.

On the whole, the varied societies of our planet are marching, however briskly or reluctantly, in lock step with an America of laissez-faire economics, cultural pluralism and political democracy. This was and is a heady stew, and one that took Western Europe and North America four or five generations to absorb. To expect Argentina or Indonesia or China or Ukraine to swallow such changes in a far shorter time is probably asking too much. No wonder we hear the creakings and crashings of the structures of the post-1945 world order all around us.

But in the Middle East the difficulties present not just another case of traditional societies having to come to terms with the forces of modernization. The unvarnished truth is that the tensions there are of a different order of magnitude. The region extends over a vast, sprawling area, where a badly damaged though powerful and religiously driven order is locked in confrontation with global trends more penetrating and unsettling than could ever have been imagined when Muslim self-confidence was at its peak some centuries ago. What Lewis is writing about in ''What Went Wrong?'' concerns one of the greatest cultural and political divides in modern history.

Sometime around 1760, Britain, then France and America took off to another world, one that was increasingly secular, democratic, industrial and tolerant in ways that left many of the other regions gasping at the combined implications of such changes. Certain societies in parts of Latin America or India or Russia felt they had little choice but to follow suit, although hoping to brake the impacts of Western man. The Middle East, powerful a half-millennium earlier, when Europe was a bundle of inchoate, backward states and unworthy of attention, did not. Yet Europe rose while the Muslim world rested on its laurels -- until it was besieged by Western ships, armaments, iron goods and cheap textiles, to all of which it became harder and harder to respond.

The West's cultural messages, especially about democracy, made things even more difficult. Those with power in Muslim societies found it impossible to contemplate the separation of religion and state, or admit to a changed place in society for women or permit the free exchange of ideas, particularly unpleasant ideas, on the lines argued by John Stuart Mill and others. But there is even more to it than that. As Lewis shrewdly points out, the works of Mozart and Shakespeare and Voltaire have traveled around the globe, as for that matter have Stravinsky, jazz and George Orwell. But they all pretty much stop at the frontiers of the Arab world, which has shown little interest in how others think, write, compose; there are few translations of these writers and few performances of these musicians, nor are there great libraries and museums of Western art to match the impressive collections of Muslim culture in the West. (There is no presumption by Lewis here that Western or Slavic or Japanese culture is inherently superior, only that it is disturbing that this troubled part of our planet has never really cared.)

It is not that the Muslim world was totally without attempts at reform and renewal in the face of global trends, or that there was no appreciation that its own earlier superiority had vanished. In fact, Lewis is extremely good in detailing Ottoman and Arab and Iranian scholars who, from the 18th century onward, called with growing alarm for change. The sad fact is that for the most part their calls went unheeded.

Among the many reasons for such a failure discussed in this remarkably succinct account, one especially stands out. It is that the reformers split into two diametrically opposed camps: the Western-oriented movements, which sought adaptation, imitation and accommodation with modernity, though within a moderately Muslim order of things; and the conservatives, who angrily claimed that the reason for the decline was traitorous forces within their own societies, those who had strayed from the true path of the prophet. These forces, the conservatives argued, were even more sinful and deserved more punishment than the infidels themselves. It is not difficult, in reading these earlier denunciations of Arab liberals, to recall bin Laden's recent ferocious speeches against the Saudi leadership and others in the Middle East for defiling the true faith.

And yet, because ''What Went Wrong?'' was written before the Sept. 11 attacks, it has no reference to the immediate crisis, nor has it therefore any prescriptions for the United States, or the West in general. This is not a text that will directly help Donald H. Rumsfeld as he waits for his morning briefings. In a way, however, this is the book's great strength, and its claim upon our attention: for it offers a long view in the midst of so much short-term and confusing punditry on television, in the op-ed pages, on campuses and in strategic studies think tanks. My guess is that Lewis feels that should bin Laden be killed, his Qaeda network destroyed and a reasonable truce prevail in Afghanistan, the problem he describes will not have gone away, because it is a far deeper and bigger question for world society than even the awful terrorist attacks on the United States late last summer.

What, then, is to be done? At the end of the day, Lewis argues, the answer lies within the Muslim world itself. Either its societies, especially those in the Middle East, will continue in ''a downward spiral of hate and spite, rage and self-pity, poverty and oppression,'' with all that implies for a horrible and troubled future; or ''they can abandon grievance and victimhood, settle their differences and join their talents, energies and resources in a common creative endeavor'' to the benefit of themselves and the rest of our planet. Perhaps the outside world can help a bit, though probably not much. ''For the time being, the choice is their own.'' With this final sentence, and all that precedes it, Lewis has done us all -- Muslim and non-Muslim alike -- a remarkable service.

Paul Kennedy is a professor of history at Yale University and the author or editor of 15 books, including ''The Rise and Fall of the Great Powers.''