The civil war, 1918-20
Following the Treaty of Brest-Litovsk, which ended Russia's part in WW1 in march 1918, political opposition groups joined to create force of 'whites'. These were supported by Britain, France and the USA. In March 1918, Bolsheviks moved their capital to Moscow in view of growing threat of 'whites' in the south..
The civil war cost around 10 million lives. However, the Bolshevik 'reds' had geographical advantages, better communications and superior organisation (under Trotsky).
By the end of the 1920s, the Bolsheviks controlled most of the former Russian empire.
The war continued into 1921 as a nationalist struggle against polish armies. A polish invasion of Western forces had been defeated at Kiev in May 1920; however a subsequent Polish victory led to the Treaty of Riga(March 1921). Granting self-rule to Poland and other nationalities.