Slovenia has a long history as a nation dating back to the fall of the Roman Empire when Germanic tribes migrated into the region. In 1918 after World War I, Slovenia joined the new State of Slovenes, Croats and Serbs which later united with Serbia and Montenegro to form the Kingdom of Yugoslavia in 1918. Economic and social crisis in the late 1980s led to resistance against Serbian domination and centralization, and in 1991 Slovenia declared independence after an overwhelming vote for sovereignty in a 1990 plebiscite.