Evacuation of Polish civilians from the USSR in World War II

Following the Soviet invasion of Poland at the onset of World War II, in accordance with the Nazi–Soviet Pact against Poland, the Soviet Union acquired more than half of the territory of the Second Polish Republic or about 201,000 square kilometres (78,000 sq mi) inhabited by more than 13,200,000 people. Within months, in order to de-Polonize annexed lands, the Soviet NKVD rounded up and deported between 320,000 and 1 million Polish nationals to the eastern parts of the USSR, the Urals, and Siberia.

Source: Wikipedia — Evacuation of Polish civilians from the USSR in World War II (CC BY-SA 4.0)