Five years ago the United States was freshly embarked on a war, of sorts. It was a war made possible by modern technology and made attractive to modern sensibilities. It was a war waged by people who thought their aim was worth killing for but not dying for. The aim, President Clinton said, was to build a “democratic, multiethnic Balkans region.”

The disintegration of Yugoslavia, which began when the Cold War ended, had demonstrated that “Europe” is still just a geographic expression, not a noun denoting a competent political entity. Europeans had failed to cope with the Continent’s worst violence since 1945, including the 1995 massacre of 8,000 at Srebrenica, carried out while U.N. peacekeeping forces loitered a few miles away. So the United States led a NATO intervention, without U.N. authorization.

The aim was to stop “ethnic cleansing” in Kosovo by rampaging Serbs against the ethnic Albanians, who are mostly Muslims and constitute 90 percent of Kosovars. More precisely, the aim was to do whatever could be done to stop it from 15,000 feet–meaning, only with air power and without casualties.

The United States conducted most air operations from that altitude and said it would not use ground forces. As a result, the initial consequence of intervention was an acceleration of ethnic cleansing. U.S. officials expected the bombing to dissuade Serbia in a week. It took 78 days.

There were no U.S. casualties. It is impossible to know, but necessary to wonder, whether America’s waging a war this way deepened the conviction of Osama bin Laden and others that America was so casualty-averse it could be struck with impunity.

One aim and effect of U.S. intervention in the Balkans–a kind of blurry border where Islam and Christianity meet–was to protect Muslims from persecution. America’s harvest of gratitude has not been bountiful.

Sir Michael Howard, the military historian, suggests three rules about intervening in civil wars: (1) Don’t. (2) If you do, pick a side. (3) Make sure your side wins. The United States and NATO disregarded the first and violated the second by not favoring independence for Kosovo, so the third was irrelevant.

That was then. This is now: Several weeks ago, in two days of rioting, ethnic Albanian mobs in Kosovo continued their own ethnic cleansing. They attacked Serbs’ villages and churches. The violence, the worst in five years, erupted when an Albanian boy said that two other boys had drowned in a river after some Serbs sicced a pit bull on them. Serbs say the boys drowned in an accident.

In any case, the ensuing violence killed 19–11 of them Kosovar Albanians–and injured more than 900. Thousands were left homeless. Albanians also burned Orthodox churches and monasteries in Kosovo. In response, Serbs burned Belgrade’s only mosque. At least that won’t happen again.

Kosovo, which today is still a province of Serbia, demands independence in the name of ethnic self-determination. But granting independence now might seem like a reward for efforts to “cleanse” Kosovo of Serbs.

Self-determination acquired legitimacy from Woodrow Wilson’s endorsement of it. However, Wilson’s Secretary of State Robert Lansing wondered: “When the president talks of ‘self-determination’ what unit does he have in mind? Does he mean a race, a territorial area, or a community?”

The 11th of Wilson’s Fourteen Points said that “relations of the several Balkan states to one another [should be] determined by friendly counsel along historically established lines of allegiance and nationality; and international guarantees of the political and economic independence and territorial integrity of the several Balkan states should be entered into.” More than eight decades later, that “friendly counsel” is still a work in progress. So is ethnic cleansing, five years after a war, of sorts, to stop it.

Which brings us back to the Fallujah barbarism. It, in turn, suggests just how long might be the “long, hard slog” in Iraq that Don Rumsfeld anticipates. But, then, surely America has already had a long, hard education about the world’s intractability.

In 1915 Walter Lippmann, a young public intellectual, wrote: “When you consider what a mystery the East Side of New York is to the West Side, the business of arranging the world to the satisfaction of the people in it may be seen in something like its true proportions.” Three years later Lippmann, then 29, was among the many experts who sailed with President Wilson to the Paris Peace Conference. It was held to tidy up after “the war to end war”–the war waged, Wilson had said, to make the world “safe for democracy.”

The conference invented Yugoslavia.