The "Einsatzgruppe VI" was formed in the town before it entered several Polish cities, including Poznań, Kalisz and Leszno, to commit various crimes against Poles during the German invasion of Poland, which started World War II. During World War II the Germans brought numerous forced laborers, both men and women, from Poland and the Soviet Union to the town. There was no fighting for the town in 1945 during World War II even though the town was declared a fortress ("Festung") in an attempt to block the Red Army's route to Berlin. The nearly empty town was burned down by the Red Army. The postwar German–Polish border ran along the Oder, separating the "Dammvorstadt" on the eastern bank – which became the Polish town of Słubice – from the rest of Frankfurt. While part of communist East Germany, Frankfurt was administered within Bezirk Frankfurt (Oder). It became part of the reconstituted state of Brandenburg with German reunification in 1990.