Polish population transfers in 1944–1946
The Polish population transfers in 1944–1946 from the eastern half of prewar Poland (also known as the expulsions of Poles from the Kresy macroregion), were the forced migrations of Poles toward the end and in the aftermath of World War II. These were the result of a Soviet Union policy that had been ratified by the main Allies of World War II. Similarly, the Soviet Union had enforced policies between 1939 and 1941 which targeted and expelled ethnic Poles residing in the Soviet zone of occupation following the Nazi-Soviet invasion of Poland. The second wave of expulsions resulted from the retaking of Poland from the Wehrmacht by the Red Army.
Source: Wikipedia — Polish population transfers in 1944–1946 (CC BY-SA 4.0)