On the night of February 9-10, 1940 the Soviet Union began the forceful deportation of Polish citizens from eastern Poland to Siberia and other parts of the Soviet Union. Officers, policemen, civil servants, landowners, members of the middle class or landowning farmers were the first who were deported.
The fourth and last mass deportation ended but a few hours before the German invasion of the USSR in June 1941. In total, around 330,000 Polish citizens: Poles, Jews, Byelorussians, and Ukrainians were deported to Kazakhstan, Uzbekistan and Siberia. Many of them did not survive the journey or their exile in Siberia or Kazakhstan because of unbearable conditions and treatment by the Soviet Union.
Nazi Germany also forced Poles to migrate. By the Spring of 1941, at least 840,000 people were brutally uprooted from their homes and stripped of all their possessions.
From November 1942 to August 1943 300 Polish villages in the Zamosc region where 110,000 Poles lived underwent extremely brutal resettlement. In 1944, after the collapse of the Warsaw Uprising followed the mass exodus of several hundred thousand Varsovians.
In the autumn of 1944 began resettlement of Poland’s eastern lands. Poles who lived to the East of the Bug River (no longer on Polish territory after the Allies changed Poland’s eastern border) were moved Westward, and Polish Ukrainians and Belarusians were sent Eastward.
Source and more information here:
https://ww2.pl/forced-migration-and-resettlement-of-poles
Photo:Warsaw’s civilian population was removed from the city since the start of the Warsaw Uprising in August 1944. They were sent mostly to a transit camp in Pruszkow, and from there transported to forced labor in the Reich or to concentration camps including Auschwitz, Mauthausen and Gusen. Pictured: columns of Warsaw residents reach the camp in Pruszkow, September 1944. Photo: Museum of Warsaw