By March 1920, it was obvious that Soviet Russia would attack Baku. Vladimir Lenin said that the invasion was justified as Soviet Russia could not survive without Baku's oil. Independent Azerbaijan lasted only 23 days 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.