In the first multiparty elections held in 1990, the ruling League of Communists was solidly defeated. The HDZ (Croatian Democratic Community) won the largest share of the vote. HDZ received 42% of the popular vote, but took 58% of the seats in parliament which set the stage for Stipe Mesic to become prime minister. Tudjman, who was leader of the HDZ became president. Under his leadership, Croatia's constitution was amended, street names and state symbols were changed, and in December 1990 the status of Serbs was changed from "constituent nation" to "national minority."
Moderate Serb parties were weakened, and those Serbs that wished to remain part of Yugoslavia and viewed Belgrade as their protector gained influence within the Serb community. The Serb populations in the Krajina region—descendants of those who had left the Ottoman Empire in 1690—declared their autonomy, labeling the new Zagreb regime as Ustaša. From Knin the center of the autonomy movement expanded to include almost one fifth of Croatian territory, though less than 5% of its population. The goal of its leaders was to remain part of a state in which Serbs were a majority---whether it was to be Yugoslavia, "Greater Serbia" or as a last resort, their own republic. Croats were to be expelled or murdered.
Serbs boycott Croatian referendum
When Croatia held a referendum on independence, Krajina Serbs boycotted the process and held their own referendum, thus reaffirming their commitment to Yugoslavia. Similar sentiments were expressed in Slavonia, Croatia's right bank territory on the Danube River that forms its border with Serbia.
In May 1991, in Borovo Selo, a community close to the Danube and the border city of Vukovar, a major firefight between Serbian irregulars and Croatian police left at least fifteen people dead.