 Complete the following phrase:  Following the German invasion of 1939, Greater Poland was incorporated into Nazi Germany, becoming the province called , later Reichsgau Wartheland  being the German name for the Warta river. The Polish and Jewish population was classified by Nazis as subhuman and subjected to organized genocide, involving mass murder and ethnic cleansing, with many former officials and others considered potential enemies by the Nazis being imprisoned or executed, including at the notorious 