There is I think one important point which has not been mentioned. The territories pursued by Stalin in 1939-1941 had nearly all been longstanding possessions of the Russian Empire. The only exception was eastern Galicia, which had belonged to the now-extinct Republic of Poland, and before that to the disintegrated Austrian Empire.
Kars had only been acquired by Russia in 1878. Bessarabia, Finland, Courland, Lithuania, Belarus, and west Ukraine had been acquired in 1792-1815.
Kars had only been acquired by Russia in 1878. Bessarabia, Finland, Courland, Lithuania, Belarus, and west Ukraine had been acquired in 1792-1815.