All of the above, plus some.
Tito refused to allow many Serbs to return to Kosovo post WWII. Instead, he gave Kosovo Alabanians an education the Albanian language and porous borders with Albania. (Tito was fueling the communists in the Greek civil war, and thought that if he could train these Kosovo Albanians to take Albania, then Tito could become the Stalin of the Balkans. But his plan didn't work) Plus, Kosovo Albanians had the highest birthrate in Europe, and as they became more numerous, they harassed many of the Serbs to leave. Nuns were raped, priests were beaten -- even Patriarch Pavle was beaten badly enough by Albanians to be hospitalized. By the 1980's, Kosovo was virtually lawless and the Albanians did anything they wanted to Serbs. The event that took Milosevic from a nobody communist bureacrat to a leader, happened when at a televised meeting in Kosovo, a little old Serb man came up to him and complained that the Albanians had beaten him and asked what Milosevic would do to stop the Albanians from hurting him. Milosevic replied "no one will dare beat you again", and became famous for that remark. The reat is history.