Many of the conflicts between Serbs, Croats, and Muslims in Bosnia can be traced back to World War II. When Germany and Italy divided Yugoslavia among themselves in 1941, alliances within the nation shattered along ethnic lines.

Germany declared a new independent state of Croatia in 1941, and most Croatians celebrated the new state, believing that Croatia would finally be free of Serbia's dominance. Sympathetic to the Croats—who claimed to share a common ancestry with the Germans—Germany set up leader Ante Pavelic to govern the new state, and under his command the extremist nationalists called Ustase began to brutally expunge all Serbs from Croatia. Thousands of Serbs were massacred, and non-Croats, including Germans, began to complain about Ustase brutality.

As the death toll mounted, two Serbian resistance groups rose up against the Ustase and anyone else who supported the independent state...