"A SINGULAR FACT OF MODERN WAR," the historian Bruce Catton once wrote, "is that it takes charge. Once begun it has to be carried to its conclusion, and carrying it there sets in motion events that may be beyond men's control. Doing what has to be done to win, men perform acts that alter the very soil in which society's roots are nourished." Catton was writing about the Civil War, but his observation applies to most wars, and it will likely apply to the war to which we are now committed. If this conflict lasts as long as it is likely to last--as long as the president has warned us it will--it will reshape our culture and our politics. It will constitute a hinge moment in American history.

We had probably entered a time of transition even before the September 11 attack. The collapse of the dot-com economy already meant that Silicon Valley and the wonders of high technology were not going to hold the nation's attention during the next ten years the way they did during the last ten. The economic slowdown had already brought one boom to an end; the next economic recovery was bound to have different growth sectors, a different personality. George W. Bush's Washington was bound to be different from Bill Clinton's.

But September 11 brought the 1990s to a close all at once. And the ensuing war will mean that the next few years will not only feel different from the last few; they will feel dramatically different. Subjects that used to seem riveting will seem stale. Can anybody imagine why we cared about Inside.com? Can anybody remember what was so buzz-worthy about Tina Brown? Can anybody relive the excitement that greeted the release of Windows 95? Can anybody get interested in think tank reports on Social Security lockboxes or charitable choice? Are there liberals still intrigued by the disease of "affluenza" or the menace of corporate branding? For that matter, can anyone read Maureen Dowd without wincing? She was the quintessential columnist of the 1990s, brilliantly treating politics as a sitcom. But she has been struggling to adapt to an era in which politics really matters.

"What changes after a hinge is our stories of ourselves," Joel Garreau wrote recently in the Washington Post, "Who we are, how we got that way, where we're headed and what makes us tick." Garreau interviewed psychologists who study "figure/ground" reversal. That's what you get when you stare at one of those drawings of two heads facing each other in profile; first you see a black face staring left, then suddenly your perception changes and you see a white face staring right. "What had been central suddenly has become peripheral. What had been ignorable has suddenly become central," Garreau writes.

Obviously nobody knows what the future years will feel like, but we do know that the next decade will have a central feature that was lacking in the last one: The next few years will be defined by conflict. And it's possible to speculate about what that means. The institutions that fight for us and defend us against disorder--the military, the FBI, the CIA--will seem more important and more admirable. The fundamental arguments won't be over economic or social issues, they will be over how to wield power--whether to use American power aggressively or circumspectly. We will care a lot more about ends--winning the war--than we will about means. We will debate whether it is necessary to torture prisoners who have information about future biological attacks. We will destroy innocent villages by accident, shrug our shoulders, and continue fighting. In an age of conflict, bourgeois virtues like compassion, tolerance, and industriousness are valued less than the classical virtues of courage, steadfastness, and a ruthless desire for victory.

LOOKING BACK, the striking thing about the 1990s zeitgeist was the presumption of harmony. The era was shaped by the idea that there were no fundamental conflicts anymore. The Cold War was over, and while the ensuing wars--like those in Bosnia and Rwanda --were nettlesome, they were restricted to global backwaters. Meanwhile, technology was building bridges across cultures. The Internet, Microsoft ads reminded us, fostered communication and global harmony. All around the world there were people casting off old systems so they could embrace a future of peace and prosperity. Chinese Communists were supposedly being domesticated by the balm of capitalist success. Peace seemed in the offing in Northern Ireland and, thanks to the Oslo process, in the Middle East.