Before Sept. 11, the course of events in the 21st century appeared reasonably predictable. Western culture -- political, economic and social -- seemed well on its way to conquering and transforming the world. If Francis Fukuyama was a bit overheated in hailing this as heralding "the end of history," it certainly seemed to indicate the direction of future developments. Insofar as there were dangers ahead, they involved rivalries among various contenders for leadership of the globe -- notably China. But for the time being American dominance was indisputable. The idea that the whole general direction of civilization might come under serious challenge was practically unthinkable. (Let us pause here to acknowledge the prescience of Samuel Huntington.)

On Sept. 11, the world awoke to the existence of a menace from a quite unexpected direction. It turned out that we had overlooked the threat from well over 1.2 billion people, concentrated in the Middle East but with outliers as distant as Indonesia, grouped under the general sobriquet of "Islam" and calling themselves "Muslims." This vast segment of humanity gives its allegiance to the prophet Mohammed, and in the seventh and subsequent centuries had made a determined and nearly successful bid to overthrow the West and establish domination of the world. But the effort was beaten back, and in recent centuries Islam had become a cultural backwater, dominated by various local tyrannies that professed to rule in obedience to "sharia," the comprehensive and unchanging laws laid down by the Prophet. In such societies, the concept of "democracy" was simply irrelevant; "the people" didn't need to govern affairs, because all necessary governance was already provided by sharia.

Insofar as the Western world thought about Islam at all, it assumed that the processes of acculturation by the West would gradually overtake and transform it, as they had overtaken all other rival systems. It was, therefore, a tremendous shock when Sept. 11 revealed that a relatively small, but nevertheless formidable proportion of the world's Muslims (if we guessed 1 percent, that would still constitute well over 12 million people) were by no means ready to be rolled over by the West. On the contrary, by equipping themselves with such Western conveniences as plane travel, cell phones and bombs, they were prepared to strike back at their Western tormentors, and ultimately (or so they told themselves) to conquer them. Matters were not made any easier by the fact that many Western nations had grown soft, failing even to reproduce themselves in numbers sufficient to maintain their population.

President Bush decided to call this unexpected new struggle "the war against terror." It is most certainly a war, and, at least for the moment, the favorite technique of the enemy is terror -- meaning small-scale atrocities, from suicide bombs to beheadings. It is a long way from overthrowing the nations of the Western world, but it is devilishly difficult to stop.

To stop it, Bush has offered Muslims something he is confident they will perceive as better than their present life: political and economic freedom on the Western model, resulting in democracy and prosperity beyond their dreams. That is what he has offered the people of Iraq, by ousting Saddam Hussein and encouraging democratic change. It is a bold offer, and one Iraq (and after it, the world's Muslims) would do well to accept.

But the fanatics among them have no such intention. Democracy is unnecessary; sharia is the only law a Muslim needs. Who would reject it, in favor of the gross immorality so prevalent in the West? Rather, it is the West that must succumb to sharia.

That is the struggle that will dominate the 21st century, until one side or the other prevails. For the United States, it may mean only (only!) a steady drumbeat of terrorist incidents, some smaller and others quite possibly far larger than those of Sept. 11 -- not to mention the casualties that our soldiers must yet sustain in Iraq. But do not suppose we can avoid the battle by pulling out of Iraq and turning the White House over to Hillary Clinton. Our enemies in the Muslim world are going to be a lot harder to appease than that.