To simplify an incredibly complicated story:

Many dispute whether the republics of former Yugoslavia (Croatia, Bosnia and Herzegovina, Slovenia, Serbia, Montenegro, and Macedonia) could have remained together forever. But few objective observers dispute that Milosevic's violent rhetoric scared the wits out of the other republics and precipitated their secession. In 1991 and '92, troops from the mostly Serb Yugoslav National Army went to war against Slovenia, Croatia, and Bosnia following their declarations of independence.

In Bosnia, Muslims, Croats, and Serbs fought a three-way war, with atrocities committed on all sides. Paramilitary troops, organized in Serbia by Milosevic's secret police force, rampaged through the countryside. Bosnian Serb militias organized the so-called "ethnic cleansing," creating concentration camps and forcing Muslims to flee their homes. Although Milosevic disavowed his relationship with these Bosnian Serbs, he armed them and exercised a great deal of control over them.