ON 17 MARCH 2004, VIOLENCE ERUPTED between Kosovar Serbs and Albanians in Mitrovica, a flashpoint in Kosovo and a microcosm of the province's many difficulties. Over the next three days, the trouble spread throughout the UN protectorate; most incidents involved ethnic Albanian mobs targeting minority residents (Serbs were the main victims, but Roma and Bosnians were also affected). NATO troops, assisted by local and international police forces, eventually restored order, but not before another bloody chapter was added to the region's history: over 20 dead, hundreds of injured, thousands of displaced people, in addition to hundreds of destroyed houses and the destruction or damage of Serbian religious sites.In the days following the violence, key officials from the international community openly confessed their surprise that such acts could, once again, occur in the Balkans, especially with the continued presence of nearly 20,000 NATO (or Kosovo force, KFOR) troops and thousands of international police officers. This is a troubling reminder that some of the people who are responsible for nation-building in the Balkans either ignore the region's history, or share the mistaken belief that the mere presence of international peacekeepers can contain a tense situation that involves economic despair, political uncertainty, and the festering wounds of the past. Given the continued fragility of Kosovo and much of the western Balkans four years after the ouster of Slobodan Milosevic, it is useful to re-examine the lessons of history. Understanding the antecedents of the problems facing the Balkans can help statesmen avoid past mistakes. As a starting point, we must reconsider the unresolved question.The eastern question, or what to do with the European possessions of the Ottoman empire-or the sick man of Europe, as it came to be known in the 19th century-was supposed to have been settled by the First World War and its aftermath. The treaties of St. Germain and Neuilly (1919), Trianon (1920), and Sevres and Lausanne (1920 and 1923, respectively) dealt with the territory of the western Balkans which previously belonged to either the Habsburg or Ottoman empires. The treaties merely confirmed the existence of a new, multiethnic polity-the kingdom of Serbs, Croats, and Slovenes, or Yugoslavia. From the beginning, this was an artificial construct that was kept alive first by fears of irredentist Italy and Hungary, then by the brilliant statesmanship of Tito, and later by the false sense of relative prosperity that was maintained by the loans that allowed socialist industries to provide jobs and a respectable standard of living in the 1960s and 1970s. ButTito's death in 1980 and the economic reckoning later that decade provided the background for the resurgent nationalism of Slobodan Milosevic and his Croatian counterpart, Franjo Tudjman, and the catastrophic wars of the 1990s. Thus the eastern question was never actually solved; it merely became the Yugoslav experiment. The second World War, the advent of Tito, and the Cold War contained the latent nationalistic tensions that existed between Serbs, Croats, Bosnian Muslims, Macedonians, and Albanians. But the economic stagnation of the late 1980s and the collapse of the eastern bloc brought out the worst manifestations of Balkan nationalism.The negative consequences of the unsolved eastern question continue to linger, in spite of the NATO military intervention under US leadership that stopped the ethnic conflicts of the 1990s. The final status of Kosovo, a UN protectorate since 1999 but still nominally a part of Serbia, may be discussed in 2005, in spite of the resistance of Belgrade and, perhaps, of Serbia's traditional protector and veto-wielding member of the security council, Russia.1 Meanwhile, Montenegrin politicians have expressed their intention to hold a referendum on their continued participation in the state union of Serbia and Montenegro, the successor state to the former Yugoslavia. …