An Orthodox Christian country, Armenia was incorporated into Russia in 1828 and the USSR in 1920. Armenian leaders remain preoccupied by the long conflict with Azerbaijan over Nagorno-Karabakh, a primarily Armenian-populated exclave, assigned to Soviet Azerbaijan in the 1920s by Moscow. Armenia and Azerbaijan began fighting over the exclave in 1988; the struggle escalated after both countries attained independence from the Soviet Union in 1991. By May 1994, when a cease-fire took hold, Armenian forces held not only Nagorno-Karabakh but also a significant portion of Azerbaijan proper. The economies of both sides have been hurt by their inability to make substantial progress toward a peaceful resolution.