Ukrainian Soviet Socialist Republic
Eventually, after the creation of the Communist Party (Bolshevik) of Ukraine in Moscow, a third Ukrainian Soviet government was formed on 21 December 1919 that initiated new hostilities against Ukrainian nationalists as they lost their military support from the defeated Central Powers. Eventually, the Red Army ended up controlling much of the Ukrainian territory after the Polish-Soviet Peace of Riga. On 30 December 1922, along with the Russian, Byelorussian, and Transcaucasian republics, the Ukrainian SSR was one of the founding members of the Union of Soviet Socialist Republics (USSR).
Western Ukraine
Following the defeat of Ukrainian People's Republic (1918) in the Ukrainian–Soviet War of 1921, Western Ukraine was partitioned by the Treaty of Riga between Poland, Czechoslovakia, Hungary, and the Soviet Russia acting on behalf of the Soviet Belarus and the Ukrainian Soviet Socialist Republic with capital in Kharkiv. The Soviet Union gained control over the entire territory of the short-lived Ukrainian People's Republic east of the border with Poland. In the Interbellum most of the territory of today's Western Ukraine belonged to the Second Polish Republic. Territories such as Bukovina and Carpatho-Ukraine belonged to Romania and Czechoslovakia, respectively.
At the onset of Operation Barbarossa by Nazi Germany, the region became part of the Third Reich in 1941. The southern half of West Ukraine was incorporated into the semi-colonial "Distrikt Galizien" (District of Galicia) created on August 1, 1941 (Document No. 1997-PS of July 17, 1941 by Adolf Hitler) with headquarters in Chełm Lubelski, bordering district of General Government to the west. Its northern part (Volhynia) was assigned to the "Reichskommissariat Ukraine" formed in September 1941. Notably, the District of Galicia was a separate administrative unit from the actual "Reichskommissariat Ukraine" with capital in Rivne. They were not connected with each other politically. Bukovina was controlled by the pro-Nazi Kingdom of Romania. After the defeat of Germany in World War II, in May 1945 the Soviet Union incorporated all territories of current Western Ukraine into the Ukrainian SSR.