After taking control of Petrograd in the October Revolution, the Bolsheviks promptly demobilized the Russian army. Now effectively defenceless, Russia was forced to accept a ruinous treaty at Brest-Litovsk in March, 1918, ceding vast areas of territory to the Central Powers. They were soon embroiled in a complex civil war. The main opposition of the Bolsheviks (the Red Army) were the White Army, a loose alliance of nationalistic and monarchist forces. Concerned by the loss of their Russian ally and the rise of communism, the Western powers sporadically intervened to assist the White Army, converging on the Soviet heartland round Moscow-St Petersburg from bases in the north, far east and south of Russia. After Germany’s defeat in World War I, the Allies withdrew their ‘interventionist’ forces from Russia, leaving the Whites unsupported. The decisive engagements occurred in late 1919; Bolshevik forces lifted a western-supported siege of Petrograd by Latvian separatists, and separate White armies were defeated and driven back to Siberia and Crimea. While mopping up continued in Siberia and Central Asia until 1923, the remnants of the main army were forced out of Crimea in November 1920. The Bolsheviks inherited a vast country in ruins.