THE UNITED STATES and its NATO allies have accomplished something of lasting importance in Kosovo. Yes, shaping the peace will be difficult, and many problems lie ahead. Yes, Slobodan Milosevic will try to make trouble again, if not in Kosovo then elsewhere. What was achieved was not a perfect victory. But it was a remarkable success, a fruit of allied unity that, if not squandered now, will further the cause of democracy and peace in Europe and beyond.

It's puzzling that so many people in Washington seem unable to accept this accomplishment. "This is certainly no victory," Indiana Republican Rep. Mark Souder said yesterday as he sought to prevent the United States from participating in a Kosovo peacekeeping force. "If this is a victory, what would defeat look like?" Perhaps the question was rhetorical, but we'd like to take a crack at answering it nonetheless.

Defeat would have left Mr. Milosevic in control of Kosovo, with a million Kosovars in refugee camps as winter approached, destabilizing Macedonia, Albania, Greece, Montenegro and maybe Hungary and Italy, too. Defeat would have been the phony deal that many detractors expected Mr. Clinton to settle for and then portray as victory. Defeat might have been a partition of Kosovo, which so many experts during the past two months counseled as the best possible arrangement NATO could salvage from its strategically flawed campaign. Defeat would have been the triumph of evil: Slobodan Milosevic orchestrating a campaign to expel an entire nation, and then getting away with it.

Mr. Milosevic did orchestrate terrible atrocities, it is true. But he did not get away with it. He has been indicted for crimes against humanity and will surely now be shunned. His people know they will receive little help in rebuilding as long as he remains in power. With his military greatly diminished, he will be less well placed to threaten others even if he remains in power. And the Kosovars will be going home, even without the passports that Serbian troops methodically confiscated. Mr. Milosevic had a plan to permanently change the demography of Kosovo; that plan will fail.

Given the terrible suffering the Kosovars have endured, the casualties among innocent Serb civilians and the challenge of reconstruction, there can be no rejoicing now. Nor were NATO's tactics beyond criticism. Stronger and more attentive diplomacy and fewer empty threats in the preceding years might have made this war unnecessary. But it's also possible that smarter diplomacy would have done no good at all. Among those who so easily draw a connection between NATO's perceived mistakes and the imperfections of today's result, there is a measure of sloppy thinking.

It is said, for example, that Mr. Clinton erred in vowing not to use ground troops. But the threat of ground troops would not likely have deterred Mr. Milosevic in the absence of actual deployments; and deployments would have taken so long that he could easily have completed his campaign of terror in any case. It is said that NATO acted immorally in bombing from such heights while Kosovars suffered. If many civilians could have been saved by putting more pilots at risk, that might be so; but again, the evidence is frail and disputable. There are great complaints now that Mr. Milosevic remains in power; but how many of the complainers supported the all-out invasion of Belgrade that alone could have guaranteed his removal?

The facts are that Mr. Milosevic began his armed campaign against Kosovo civilians in February 1998. His war of terror ebbed and flowed thereafter as NATO attention waxed and waned, but it never stopped. The Serbian strongman bet that he could empty Kosovo of its ethnic Albanians one village at a time and that NATO would not respond. When that proved wrong, he bet that he could intensify his atrocities and ride out NATO's bombing campaign -- that NATO would crack before he did.

He was wrong again. NATO did not crack, and neither did Mr. Clinton. The results will be studied around the world, and the lessons people draw will bolster the United States and the values that, at its best, this country stands for.