Polish areas annexed by Soviet Union

Under the terms of the Molotov-Ribbentrop Pact, adjusted by agreement on 28 September 1939, the Soviet Union annexed all Polish territory east of the line of the rivers Pisa, Narew, Bug, and San, except for Wilno country with its capital Wilno (Vilnius), which was given to Lithuania, and the Suwalki region, which was annexed by Germany. These territories were largely inhabited by Ukrainians and Byelorussians, with large minorities of Poles and Jews. The total area, including the area given to Lithuania, was 201,000 square kilometres, with a population of 13.5 million, of which about 5.2-6.5 million were ethnic Poles.

During 1939-1941 at least 1.8 million of the people inhabiting the region were killed or deported by the Soviet regime, from which at least 60% were Poles, and second the largest group were Jews.