The September Days refers to a period during the Russian Civil War in September 1918 when Armenian inhabitants of Baku, Azerbaijan, were massacred by Enver Pasha's Army of Islam and their local Azerbaijani allies when they captured the soon-to-be capital of the Azerbaijan Democratic Republic. According to most estimates, approximately 10,000 ethnic Armenians were killed in the violence, although some sources claim the number to be as high as 30,000. The massacre is said by some scholars to have been carried out in retaliation for the earlier March Days. It was the last major massacre of World War I.