The Nagorno-Karabakh region has been populated by Armenians for a long time. The area has been disputed by Armenia and Azerbaijan since 1918. After the Soviet Union established control over the area, in 1923 it formed the Nagorno-Karabakh Autonomous Oblast (NKAO) within the Azerbaijan SSR. In the final years of the Soviet Union, the region again became a source of dispute between Armenia and Azerbaijan, resulting in the Nagorno-Karabakh War from 1988–1994.