The Nagorno-Karabakh conflict is the longest-running in post-Soviet Eurasia. In 1988, ethnic Armenians living in Nagorno-Karabakh demanded the transfer of what was then the Nagorno-Karabakh Autonomous Oblast (NKAO) from Soviet Azerbaijan to Armenia. As the Soviet Union collapsed, tensions grew into an outright war. When fighting ceased in 1994, Nagorno-Karabakh and seven adjacent districts were wholly or partially controlled by Armenian forces. More than a million people had been forced from their homes: Azerbaijanis fled Armenia, Nagorno-Karabakh and the adjacent territories, while Armenians left homes in Azerbaijan.
From 1994 until 2020, intermittent deadly incidents, including the use of attack drones and heavy weaponry on the front lines and activities of special operations forces, demonstrated the ever-present risk that war would reignite. In April 2016, four days of intense fighting at the line of separation shook the region, killed hundreds on both sides, and foreshadowed what was to come.