A conflict fought in Russia between the anti-communist White Army supported by some Western powers, and the Red Army of the Soviets in the aftermath of the Russian Revolution of 1917. It is sometimes referred to as the War of Allied Intervention. Counter-revolutionary forces began organized resistance to the Bolsheviks in December 1917, and clashed with an army hastily brought together by Trotsky. In northern Russia a force made up of French, British, German, and US units landed at Murmansk and occupied Archangel (1918–20). Nationalist revolts in the Baltic States led to the secession of Lithuania, Estonia, Latvia, and Finland, while a Polish army, with French support, successfully advanced the Polish frontier to the Russian Ukraine, gaining an area not re-occupied by the Soviet Union until World War II. In Siberia, where US and Japanese forces landed, Admiral Kolchak acted as Minister of War in the anti-communist ‘All Russian Government’ and, with the aid of a Czech legion made up of released prisoners-of-war, gained control over sectors of the Trans-Siberian Railway. He, however, was betrayed by the Czechs and murdered, the leadership passing to General Denikin, who sought to establish (1918–20) a ‘United Russia’ purged of the Bolsheviks. In the Ukraine Denikin mounted a major offensive in 1919, only to be driven back to the Caucasus, where he held out until March 1920. In the Crimea the war continued under General Wrangel until November 1920. A famine in that year caused further risings by the peasants against the communists, while a mutiny of sailors at Kronstadt was suppressed by the Red Army. To win the war, Lenin imposed his ruthless policy of ‘war communism’. Lack of cooperation between counter-revolutionary forces contributed to their final collapse and to the establishment of the Soviet Union.