who seized ukraine and belarus to form the soviet union
History of Soviet Russia and the Soviet Union (1917–27) The frontiers between Poland, which had established an unstable independent government following World War I, and the former Tsarist empire, were rendered chaotic by the repercussions of the Russian revolutions, the civil war and the winding down World War I. Poland's Józef Piłsudski envisioned a new federation (Międzymorze), forming a Polish-led East European bloc to form a bulwark against Russia and Germany, while the Russian SFSR considered carrying the revolution westward by force. When Piłsudski carried out a military thrust into Ukraine in 1920, he was met by a Red Army offensive that drove into Polish territory almost to Warsaw. However, Piłsudski halted the Soviet advance at the Battle of Warsaw and resumed the offensive. The "Peace of Riga" signed in early 1921 split the territory of Belarus and Ukraine between Poland and Soviet Russia.