Why were ethnic tensions renewed in the balkans at the end of the 1980's?

In 1991 and 1992, Yugoslavia disintegrated under the pressures of ethnic conflict, economic issues, and the demagoguery of Serbian President Slobodan Milosevic. The secessions of Slovenia and Croatia triggered warfare in both new nations, with the United Nations inserting a peacekeeping force, the U.N. Protective Force (UNPROFOR), in mid-1992 to stabilize the situation. The U.N. further imposed an arms embargo on the region, seeking to dry up the flow of arms to the combatants. Serbian forces executed widespread “ethnic cleansing” in occupied areas, creating horrific scenes of refugees and concentration camps that seemed unthinkable in modern Europe.