The Russian Revolution of 1917 overthrew the Tsarist autocracy and established the world's first socialist state. Years of war had devastated Russia and unrest was growing due to food shortages and heavy casualties. In March 1917, widespread strikes and protests in Petrograd led the Tsar to abdicate. A provisional government took over but struggled to assert control as workers councils (Soviets) gained power. In October, the Bolsheviks seized power on behalf of the Soviets and established the Soviet Union under Vladimir Lenin. A civil war then erupted between the Bolsheviks and opposing forces. After several years of fighting, the Communists emerged victorious by 1921.