The Siberian intervention was a theater of the Allied intervention in the Russian Civil War which took place in Siberia, the Russian Far East, and Mongolia from 1918 to 1920.
Following the Revolt of the Czechoslovak Legion in Siberia, the chief Entente powers of Britain and France decided to intervene in the Russian Civil War on the anti-Bolshevik side to help the Czechoslovak Legion evacuate to the Western Front, to prevent the Allied military stockpiles in Russia from falling into German or Bolshevik hands, and to resurrect the Eastern Front by installing a White Russian-backed government in power. The United States also agreed to furnish 5,000 US Army troops for the "Polar Bear Expedition" to Arkhangelsk and 10,000 more troops to take part in an expedition to Siberia, where they would help the Czechs. In July 1918, the Republic of China also agreed to intervene, sending 2,000 Chinese troops to Russia in August 1918, and occupying Mongolia and Tuva. President Woodrow Wilson suggested that Japan should send 7,000 troops to aid the Allied campaign, but Japan instead sent 70,000 troops. The first Allied troops, a British battalion, arrived at Vladivostok on 3 August 1918, followed by 500 French Army troops from French Indochina in August 1918. 4,192 Canadian Army troops arrived at Vladivostok on 26 October 1918, and 2,500 Italians who had been captured while fighting in the Austro-Hungarian Army formed the Legione Redenta to fight for Allied Italy. The Allies doubted Japan's intentions behind sending such a large force to Russia, fearing that Japan sought to conquer Manchuria for itself. The underlying chaos and suspicion hampered cooperation between the Allied forces, and most of the Allied soldiers retained defensive positions throughout the intervention, guarding the Trans-Siberian Railway as the Czechoslovaks made their way towards Vladivostok. In October 1918, Czechoslovakia was proclaimed an independent state, depriving the Czechoslovak soldiers of any will to fight, as they merely wished to return home to their newly-free country. In the summer of 1919, the White Russian regime in Siberia collapsed, the Canadians withdrew by June 1919, the British withdrew by November 1919, the White Russian admiral Alexander Kolchak was betrayed to the Bolsheviks by the Czechoslovaks in February 1920 in exchange for safe passage to Vladivostok, and the next few months saw most of the remaining Allied forces withdraw from Vladivostok. However, the Japanese remained behind due to their territorial ambitions in Siberia and the Russian Far East, and they supported the Provisional Priamurye Government until October 1922, when the Western powers persuaded the Japanese to withdraw as well, ending the Allied intervention in Siberia.