The postwar population transfers , targeting Polish nationals , were part of an official Soviet policy that affected more than one million Polish citizens , who were removed in stages from the Polish areas annexed by the Soviet Union . After the war , following Soviet demands laid out during the Tehran Conference of 1943 , the Kresy macroregion was formally incorporated into the Ukrainian , Belarusian and Lithuanian Republics of the Soviet Union . This was agreed at the Potsdam Conference of Allies in 1945 , to which the acting Government of the Republic of Poland in exile was not invited
Potsdam Conference
Potsdam Conference
Polish population transfers (1944–1946)