The last Russian Tsar, Nicholas II, ruled the Russian Empire until his abdication in March 1917 in the aftermath of the February Revolution, due in part to the strain of fighting in World War I which lacked public support. A short-lived Russian Provisional Government took power, to be overthrown in the October Revolution (N.S. 7 November 1917) by revolutionaries led by the Bolshevik leader Vladimir Lenin.
The Soviet Union was officially established in December 1922 with the union of the Russian, Ukrainian, Byelorussian, and Transcaucasian Soviet republics- each ruled by local Bolshevik parties. Despite the foundation of the Soviet state as a federative entity of many constituent republics, each with its own political and administrative entities, the term "Soviet Russia" – strictly applicable only to the Russian Federative Socialist Republic – was often applied to the entire country by non-Soviet writers and politicians.