On 20–23 October 1939 alone, the German police and Einsatzgruppe VI carried out mass public executions of some 300 Poles in various towns in the region, i.e. Gostyń, Kostrzyn, Kościan, Kórnik, Krobia, Książ Wielkopolski, Leszno, Mosina, Osieczna, Poniec, Śmigiel, Śrem, Środa and Włoszakowice, to terrorize and pacify the Poles.

[8] Due to poor feeding and sanitary conditions, epidemics spread in those camps, which, combined with frequent executions, led to a high mortality rate.

[8] The Gauleiter and Reichsstatthalter of Reichsgau Wartheland, native-born Arthur Greiser,[9] embarked on a program of complete removal of the formerly Polish citizenry upon his nomination by Heinrich Himmler.

[11] He also authorized the clandestine operation of exterminating 100,000 Polish Jews (about one-third of the total Jewish population of Wartheland),[12] in the process of the region's complete "Germanization".

[13] In the first year of World War II, some 630,000 Poles and Jews were forcibly removed from Wartheland and transported to the occupied General Government (more than 70,000 from Poznań alone) in a series of operations called the Kleine Planung covering most Polish territories annexed by Germany at about the same time.

[14] By the end of 1940, some 325,000 Poles and Jews from the Wartheland and the so-called Polish Corridor were expelled to General Government, often forced to abandon most of their belongings.

[8] In 1941, the Nazis expelled a further 45,000 people, and from autumn of that year, they began killing Jews by shooting and in gas vans, at first spasmodically and experimentally.

Greiser wrote in November 1942: "I myself do not believe that the Führer needs to be asked again in this matter, especially since at our last discussion with regard to the Jews he told me that I could proceed with these according to my own judgement.

[25] The Polish resistance movement was active in the region, including the Union of Armed Struggle, Bataliony Chłopskie, Gray Ranks and Home Army.

[35] From August 1944 to January 1945, the Germans used hundreds of thousands of Poles as forced labour to build fortifications in the region ahead of the advancing Eastern Front.

[citation needed] The remaining ethnically German population was expelled to Allied-occupied Germany after the war ended in accordance with the Potsdam Agreement.