23 months until the Bolshevik 11th Soviet Red Army invaded it, establishing the Azerbaijan SSR on 28 April 1920. Although the bulk of the newly formed Azerbaijani army was engaged in putting down an Armenian revolt that had just broken out in Karabakh, Azerbaijanis did not surrender their brief independence of 1918–20 quickly or easily. As many as 20,000 Azerbaijani soldiers died resisting what was effectively a Russian reconquest. Within the ensuing early Soviet period, the Azerbaijani national identity was finally forged. On 13 October 1921, the Soviet republics of Russia, Armenia, Azerbaijan, and Georgia signed an agreement with Turkey known as the Treaty of Kars. The previously independent Republic of Aras would also become the Nakhchivan Autonomous Soviet Socialist Republic within the Azerbaijan SSR by the treaty of Kars. On the other hand, Armenia was awarded the region of Zangezur and Turkey agreed to return Gyumri (then known as Alexandropol). During World War II, Azerbaijan played a crucial role in the strategic energy policy of the Soviet Union, with 80 percent of the Soviet Union's oil on the Eastern Front being supplied by Baku. By the Decree of the Supreme Soviet of the USSR in February 1942, the commitment of more than 500 workers and employees of the oil industry of Azerbaijan were awarded orders and medals. Operation Edelweiss carried out by the German Wehrmacht targeted Baku because of its importance as the energy (petroleum) dynamo of the USSR. A fifth of all Azerbaijanis fought in the Second World War from 1941 to 1945. Approximately 681,000 people with over 100,000 of them women, went to the front, while the total population of Azerbaijan was 3.4 million at the time. Some 250,000 people from Azerbaijan were killed on the front. More than 130 Azerbaijanis were named Heroes of the Soviet Union. Azerbaijani Major-General Azi Aslanov was twice awarded the Hero of the Soviet Union. Independence Following the politics of glasnost, initiated by Mikhail Gorbachev, civil unrest and ethnic strife grew in various regions of the Soviet Union, including Nagorno-Karabakh, an autonomous region of the Azerbaijan SSR. The disturbances in Azerbaijan, in response to Moscow's indifference to an already heated conflict, resulted in calls for independence and secession, which culminated in the Black January events in Baku. Later in 1990, the Supreme Council of the Azerbaijan SSR dropped the words "Soviet Socialist" from the title, adopted the "Declaration of Sovereignty of