The Armenian-Azerbaijani war (1918–1920) was a conflict that took place in the South Caucasus in regions with a mixed Armenian-Azerbaijani population, broadly encompassing what are now modern-day Azerbaijan and Armenia. It began during the final months of World War I and ended with the establishment of Soviet rule.
The conflict took place against the backdrop of the Russian Civil War and the partition of the Ottoman Empire. Mutual territorial claims, made by the newly formed Azerbaijan Democratic Republic and the Republic of Armenia, led to their respective support for Azerbaijani and Armenian militias in the disputed territories. Armenia fought against Azerbaijani militias in the Erivan Governorate of the former Russian Empire, while Azerbaijan fought Armenian claims to the Karabakh region. The war was characterized by outbreaks of massacres and ethnic cleansing (such as the March Days, the September Days, the Shusha massacre, and more broadly, the massacres of Azerbaijanis in Armenia), which changed the demographics of the region.
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