Population exchange between Poland and Soviet Ukraine

The population exchange between Poland and Soviet Ukraine at the end of World War II was based on a treaty signed on 9 September 1944 by the Ukrainian SSR with the newly-formed Polish Committee of National Liberation (PKWN). The exchange stipulated the transfer of ethnic Ukrainians who had Polish citizenship before September 17, 1939 to the Ukrainian SSR and of ethnic Poles and Jews who had Polish citizenship before September 17, 1939 (date of the Soviet Invasion of Poland) to post-war Poland, in accordance with the resolutions of the Yalta and Tehran conferences and the plans about the new Poland–Ukraine border.

Source: Wikipedia — Population exchange between Poland and Soviet Ukraine (CC BY-SA 4.0)