In 1987, Yugoslavia was made up of six republics - Serbia, Croatia, Montenegro, Slovenia, Bosnia-Herzegovina, and Macedonia.
They had lived in peace for many years under the previous president, Tito.
But when Tito died, the hatred between the republics came to the surface.
In particular, many of the smaller republics wanted to break away from Serbia - the biggest of them all.
Milosevic became president in 1989 by promising the Serbs that he would never allow them to lose out.