Depends, this, on the section of '38 gives some cursory info on the land-grabs And this details the Soviet-Polish war of 1920 in which the fledgling Soviet republics sought to liberate lands stolen by the Germans and granted to the reactionary nationalists during ww1's Treaty of Brest-Litovsk.
They're good rough starts on the subjects to get an idea of the bigger picture of the region.