Wednesday evening, NATO attacked a sovereign nation for the first time in the alliance's 50-year history. The initial strikes against Yugoslavia, carried out by B-2 "stealth" bombers and cruise missiles, were designed to suppress air-defense systems and other military targets and are the first steps in a campaign that is expected to last several days. They were launched reluctantly, after months of failed negotiations with Yugoslav authorities that were intended to end the government's war against ethnic Albanians in the province of Kosovo.

There must be no mistake. Responsibility for this attack lies squarely in Belgrade. The government of Yugoslav President Slobodan Milosevic has defied Western efforts to bring peace to Kosovo. Instead, it has reinforced its security presence in the troubled province and engaged in a ruthless campaign against Albanian separatists and anyone suspected of providing them support. In more than a year of fighting, over 2,000 Kosovars have been killed -- many in savage fashion -- and hundreds of thousands of others have been driven from their homes. Accusations of war crimes have already been raised against Serb forces in the region.

"Operation Allied Force" has been justified on two grounds: averting a human catastrophe and preventing a wider war. Both are reasonable arguments; both are applicable in this case. But there is a third reason as well: Western credibility. Throughout the months of negotiations over Kosovo, the West threatened the use of military force if peace talks broke down. Apparently, the Yugoslav government did not take that option seriously. It is now paying the price for its defiance.