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).
Organization of Ukrainian Nationalists
In 1940 the OUN split into two parts. The older, more moderate members supported Andriy Melnyk and the OUN-M, while the younger and more radical members supported Stepan Bandera's OUN-B. After the start of the Axis invasion of the Soviet Union on 22 June 1941 (Operation Barbarossa), the OUN-B in the person of Yaroslav Stetsko declared an independent Ukrainian state on 30 June 1941 in occupied Lviv, while the region was under the control of Nazi Germany. In response, the Nazi authorities suppressed the OUN leadership. In October 1942 the OUN-B established the Ukrainian Insurgent Army (UPA).