The Nagorno-Karabakh Autonomous Oblast voted to secede from Azerbaijan and join Armenia, triggering the First Nagorno-Karabakh War.

The Nagorno-Karabakh Autonomous Oblast (NKAO) was an autonomous oblast within the Azerbaijan Soviet Socialist Republic that was created on July 7, 1923. Its capital was the city of Stepanakert. The majority of the population were ethnic Armenians.

The First Nagorno-Karabakh War was an ethnic and territorial conflict that took place from February 1988 to May 1994, in the enclave of Nagorno-Karabakh in southwestern Azerbaijan, between the majority ethnic Armenians of Nagorno-Karabakh backed by Armenia, and the Republic of Azerbaijan with support from Turkey. As the war progressed, Armenia and Azerbaijan, both former Soviet republics, entangled themselves in protracted, undeclared mountain warfare in the mountainous heights of Karabakh as Azerbaijan attempted to curb the secessionist movement in Nagorno-Karabakh.