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).
Polish–Ukrainian War
In the beginning of the Second World War, the area was annexed by the Soviet Union and attached to Ukraine, which at that time was a republic of the Soviet Union. According to the Yalta Conference decisions, while the Polish population of Eastern Galicia was resettled to Poland, the borders of which were shifted westwards, the region itself remained within the Soviet Ukraine after the war and currently forms the westernmost part of now independent Ukraine.