During the Second World War and after, the Azerbaijan SSR, as a petroleum producer, was important in the energy policy of the Soviet Union. Following the politics of reforms called "glasnost", started by the leader of the Soviet Union Mikhail Gorbachev, riots and ethnic fighting grew in various regions of the Soviet Union, including Nagorno-Karabakh, a region of the Azerbaijan SSR. The disturbances in Azerbaijan, in response to the Soviet government's lack of response to the already tense conflict between the Azerbaijanis and Armenians, resulted in calls for independence and secession, which resulted in the massacre known as "Black January" in the capital Baku in January 1990. Azerbaijan eventually declared independence on October 18, 1991. The Soviet Union was ended on December 25, 1991.