Complex sentence: The expulsion policy was part of a geopolitical and ethnic reconfiguration of postwar Europe and, in part, retribution for Nazi Germany's initiation of the war and subsequent atrocities and ethnic cleansing in Nazi-occupied Europe.
Split into simpler sentences: The expulsion policy was part of a geopolitical and ethnic reconfiguration of postwar Europe. In part, it was retribution for Nazi Germany's initiation of the war and subsequent atrocities and ethnic cleansing in Nazi-occupied Europe.