In the southern Caucasus Mountains, thousands of ethnic Armenians have set their homes on fire as they began a mass exodus from the disputed territory of Nagorno-Karabakh, making way for Azerbaijani forces to take control of the region. The civilian withdrawal began as Russian peacekeepers arrived to oversee the transfer of power in Nagorno-Karabakh to Azerbaijan, the victor of a war with Armenia that broke out on September 27. It was the worst fighting in Nagorno-Karabakh since the breakup of the Soviet Union in the early 1990s, when conflict killed some 20,000 people and displaced a million others — most of them Azeris.