Complex sentence: Poles and Polish Jews from the Soviet Union were subject of a process called "repatriation" (settlement within the territory of post-war Poland), but those of them who were imprisoned or deported to work camps in Siberia or Kazakhstan were frequently excluded.
Split into simpler sentences: Poles and Polish Jews from the Soviet Union were subject of a process called "repatriation" (settlement within the territory of post-war Poland). This didn't apply to those of them who were imprisoned or deported to work camps in Siberia or Kazakhstan were frequently excluded.