Within the USSR, the name of the country was "Byelorussian Soviet Socialist Republic". It was declared on January 1, 1919 in Smolensk under the name of Socialist Soviet Republic of Byelorussia (SSRB). Viačasłaŭ Adamovič (Wiaczesław Adamowicz; pseudonym J. Dziergacz) planned and initiated military actions by Belarusian troops against the Soviets in Minsk and was also the founder of the partisan (military) unit, Zialony Dub (Green Oak). Some time in 1918 or 1919, Sergiusz Piasecki returned to Belarus, joining the anti-Soviet Zialony Dub, led by ataman Wiaczesław Adamowicz. When on August 8, 1919 Polish Army troops captured Minsk, Adamowicz decided to cooperate with them. Thus, Belarusian units were created and Piasecki was transferred to Warsaw school of infantry cadets. In the summer of 1920, during Polish–Soviet War, Piasecki fought in the Battle of Radzymin. The frontiers between Poland, which had established an independent government following World War I, and the former Russian Empire, were not recognized by the League of Nations. Poland's Józef Piłsudski, who envisioned a federation (Międzymorze), forming an East European bloc to form a bulwark against Russia and Germany, carried out Kiev Offensive into Ukraine in 1920, but was met by a Red Army counter-offensive that drove into Polish territory almost to Warsaw. However, Piłsudski halted the Soviet advance at the battle of Warsaw and resumed the offensive. Finally the Treaty of Riga, ending the Polish–Soviet War, divided Belarusian territories between Poland and Soviet Russia. For next two years BNR prepared for national uprising in Belarus and ceased the preparations only when the League of Nations recognised the eastern borders of Soviet Union on March 15, 1923.