Why was there a conflict in Yugoslavia?

Clear ethnic conflict between the Yugoslav peoples only became prominent in the 20th century, beginning with tensions over the constitution of the Kingdom of Serbs, Croats, and Slovenes in the early 1920s and escalating into violence between Serbs and Croats in the late 1920s after the assassination of Croatian

Explanation:

The violence erupted in Yugoslavia following the breakup of the Soviet Union in 1991. ... The ethnic violence was associated with the rise and fall of Serbian leader Slobodan Milosevic (1941–2006). For many around the world Milosevic became the human face of ethnic cleansing and violence.