This is the end logic of terror. The long age of imperialism bequeathed to this century a world full of questions of who wronged whom, and who stole whose land, and what should be done. Those questions, far from finding resolution in the half-peace of the Cold War's aftermath, roil ever more. Absent the relative stability imposed by the war of the giants, the grievances of those upon whom the giants acted out their territorial ambitions have much more room to grow.

In theory, this is not a bad thing. But there are two great problems. The first is that, in the end, the whole world was stolen from somebody, most of it repeatedly; there are claims and counterclaims and counter-counterclaims for every inch of the planet that is desirable and for much that is not. The second is that people (and the governments they form) do not like to give back what they have acquired, whether that acquisition is of dubious morality or not.

So, those with territorial claims turn to force. But here arises a third problem: By and large, the aggrieved do not possess the force necessary to win their way in open battle. Given this, a common response has been the use of terror: attacks by the aggrieved not on the soldiers of the enemy, but on the people of the enemy -- on innocent victims, chosen at random, the more innocent and the more random, the better, tactically speaking.

Given that this is murder, you would think that terrorism would have a hard time finding adherents. But tribalism is a powerful corrupting force, and so is ideology, and an awful quality of modern times has been the degree to which terror by various movements has been accepted as legitimate by those who support the goals of those movements. Communism found no difficulty persuading generations on the left that terror on the most massive scale was justified by the need to free the world from the yoke of capitalistic imperialism. Irish Americans have almost monolithically supported the IRA in its decades of bombings and killings aimed at scaring the British out of Northern Ireland. And so it goes, case by tribal or ideological case, around the world.

Of all the uses of terror, none in the past several decades has been more faddishly popular (at least on the left), and none has been accorded more respectful media coverage, than that of the Palestinians. Yes, Palestinian terrorists and terrorists on behalf of the Palestinian cause murdered innocents -- but that was understandable, the argument went. The Palestinians had been wronged. They were oppressed. They were weak. What else could they do?

Here is where we end up, with murder on a mass scale of people whose sole sin was, apparently, that they were Americans. Immediate suspicion focused on anti-Israeli (and therefore anti-American) terrorist groups. Yasser Arafat, who has championed the legitimacy of anti-Israeli terror his entire career, nonetheless was quick to express himself "completely shocked," at an attack he said he condemned, and he offered the American people condolences on behalf "of the Palestinian people."

I don't doubt Arafat's shock. And I don't think he had anything directly to do with the monstrous evil of Sept. 11. Indeed, it is possible that what happened yesterday had nothing to do with the Middle East. But this evil rose, with hideous logic, directly from the philosophy that the leaders and supporters of the Palestinian cause have long embraced and still embrace -- a philosophy that accepts the murder of innocents as a legitimate expression of a legitimate struggle.

If it is morally acceptable to murder, in the name of a necessary blow for freedom, a woman on a Tel Aviv street, or to blow up a disco full of teenagers, or to bomb a family restaurant -- then it must be morally acceptable to drive two jetliners into a place where 50,000 people work. In moral logic, what is the difference? If the murder of innocent people is for whatever reason excusable, it is excusable; if it is legitimate, it is legitimate. If acceptable on a small scale, so too on a grand.

In the West Bank city of Nablus yesterday afternoon, the Associated Press reported, thousands of Palestinians greeted news of the slaughter in New York and Washington with an impromptu street party, cheering "God is great" and distributing candy in a traditional form of celebration.

The revelers must have greeted their leader's words with some puzzlement. Was this not the ultimate expression of President Arafat's very own philosophy? Was this not a great blow -- the greatest ever -- against oppression? Was this not a necessary and good thing, as they had been taught, as they had been taught to teach their children? Is not a great good better than a small good?