Answer:
Before World War I, Yugoslavian countries were f***ed up (like today). They decided to unite in Yugoslavia, which was a monarchy. People had bad lifes, just like they did before the unification. During the World War II, Nazis occupied Yugoslavia, they created a nazi puppet state of Croatia, and they gave Bosnia to Croatia. It was controlled by the Croatian fascists, Ustašas, which was lead by Ante Pavelić. The Serbs had their own fascist movement, Četniks, lead by Draža Mihajlović. Josip Broz Tito gathered a small army of Partisans, and wanted to clear the country of Nazis and fascists. Even tho the partisans were heavily outnumbered, they won the war against German Nazis, Italian, Croatian, Serbian, Montenegrin and Bulgarian. Tito, with motto "Brotherhood and Unity" united the country again and he was praised like a God. Yugoslavia was made into one of the most developed countries of the World. Everyone had a good life, thanks to Tito, and communism, and only a small set of people didn't like Tito's regime. Those were the nationalists, the remnants of the WW2 Nazis. As soon as Tito died, they started to act. Slobodan Milošević, Serbian nationalist, took power of Yugoslavia. He wanted to create "Greater Serbia" out of Yugoslavia. He started to spread hatred amongst peoples of Yugoslavia. Franjo Tuđman, a Croatian nationalist, took control of Croatia, and did the same. Alija Izetbegović, Bosnian natioanalist did the same, too. Slovenia was the first Yugoslavian Republic to ask for indenpendence. Then Croatia did it, and Bosnia.