THE EARLIEST SEEDS of dissent took root in the Balkans long before the Slavic Serbs, Croats, and Bosnians even lived there. In A.D. 395 the Christian Church schismed (divided) into the Eastern Orthodox, or Byzantine, and the Roman Catholic Churches, splitting the mountainous region right down the middle. The Roman Catholics claimed the northern Balkans and the Eastern Orthodox took the southern ones. When the ancestors of the modern Slavs began migrating into these lands from northeastern Europe and Ukraine around A.D. 500, they adopted one religion or the other depending upon where they settled, thereby establishing the first of what would become many critical disparities.

Tribal enmities

The religions themselves created further distinctions in dialects, alphabets, and customs. The Roman Catholics introduced the northern Croats and Slovenians to the Roman alphabet while the southern Serbs...