WASHINGTON—Kosovo’s leaders—along with their European and American supporters—should not forget the lesson behind the tragedy that led to the Serbian province’s declaration of independence this week. That lesson has much more to do with the horrors of nationalism as a power-hungry ideology than with the evils, real or perceived, of the Serbs.

The contemporary conflict began with Slobodan Milosevic, an obscure member of Yugoslavia’s Communist bureaucracy, undergoing a conversion to a Serbian nationalist in the late 1980s in order to make his way to the top. By stoking Serb passions with the help of other leaders in Belgrade, Milosevic provoked a chain reaction that turned Yugoslavia into the inferno of the 1990s. By repealing Kosovo’s autonomy, Milosevic also made sure that the hatreds between the province’s Albanian majority and its Serb minority would flare up again.

It is easy to forget the genesis of the Balkan tragedy. Indeed I remember being struck, in my trips to Yugoslavia during the wars of secession, by how confused people were about who had started what—and that was relatively soon after Milosevic’s rise to power! What we are seeing today, years after the fall of Milosevic, the end of Yugoslavia and Serbia’s surrender of Kosovo to NATO, is the consequence of the diabolical sequence set in motion by a brutal despot who cloaked his ambitions with a collectivist ideology designed to bamboozle the public into believing that the nation was in peril.

But if these contemporary facts give authority to the Albanian majority’s jubilant declaration of independence, let us keep in mind that historically both sides have inflicted death and suffering on each other. And, as with so many conflicts rooted in nationalism, both sides have compelling historical claims.

The Serbs set foot in Kosovo in the 11th century in the midst of their struggle against the Byzantine Empire. That was long before Albanian nationalism emerged in the province at the end the 19th century. As the Serbs keep reminding us, Kosovo was the scene of a seminal event in the history of their nation: the battle that bears the province’s name against the Ottoman Turks. Finally, there were times when Kosovo’s Albanians sided with imperialist powers—the Turks, the Bulgarians—bent on oppressing the Serbs and took part in ethnic cleansing, especially in the latter part of the 19th century. That is partly how the Albanians became a majority in the province.

None of this excuses Serbian nationalism—an oppressive factor in the Balkans since Medieval times. It simply goes to say that conflicts between two forms of nationalism often conceal genocides, atrocities and conquests perpetrated by both sides, even if the magnitude and the frequency are greater on one side.

There is no easy solution to Kosovo. But if one delves into historical precedent, one can find certain periods in which the ethnic and tribal instincts among the Yugoslavs, or Slavs of the south, were attenuated by an environment in which people were able to go about their business without too much political intrusion. One such period was during the Austro-Hungarian empire, which was based to a large extent on free trade and decentralization—at least until the peace was shattered after a Serbian nationalist sparked off World War I by assassinating Archduke Franz Ferdinand of Austria.

The people who govern Kosovo today, starting with Prime Minister Hashim Thaci, are the same ones who in the second half of the 1990s formed the Kosovo Liberation Army (KLA), replacing the peaceful methods of leaders such as Ibrahim Rugova with killings and terrorist acts. The fact that the Kosovo war was initiated by Serbian murderers and that 1 million Albanians had to flee Kosovo in the second half of the 1990s should not make us forget the crimes of the KLA.

Since Rugova’s death, the Albanian moderates have been overshadowed by the radicals. Those radicals have been contained by the presence of NATO and the United Nations. But, having achieved their cherished ideal, are those politicians going to heed the lessons of history and establish a republic based on tolerance, pluralism and free trade to the detriment of their own nationalist penchant? Or are they going to continue the endless cycle of authoritarianism that is Kosovo’s history?

If the Kosovars end up replacing one form of nationalism with another, the recent declaration of independence will prove to be a betrayal of the wishes of ordinary Kosovars who aspire to be free and live in peace with themselves and the rest of Europe.