In the spring of 1941, as preparations were under way for the invasion of the USSR, Hitler proclaimed that a war of destruction was about to start. He called for the annihilation of the Bolshevik leadership, thus laying the foundation for the extermination of what Hitler considered to be the biological source of Bolshevism: the Jews of the USSR. The killings were to be conducted by four mobile SS units called Einsatzgruppen (action squads), each consisting of some 1,000 men. In addition to the Einsatzgruppen, there were other SS and police units commissioned to shoot Jews who were to be assembled in front of mass graves dug by the Jews themselves. On many occasions after the military campaign started in June 1941, the German army was called on to provide support to the SS and police units. Thus, the total number of Germans involved in the mass shootings of Jews was around 30,000.
Massive Population Shifts
On July 2, 1941, Reinhard Heydrich, head of Germany's Sicherheitsdienst (SD; Security Service) and an instrumental figure in organizing the extermination of the Jews, issued his Commissars' Order, according to which all Jews in official positions in the Soviet administration were to be executed. However, the Einsatzgruppen commanders broadly interpreted this order to mean all adult male Jews. Large numbers of them were immediately shot regardless of whether they held official Soviet positions. In August 1941 the killings were expanded to include Jewish women and children. For example, on August 1, 1941, Heinrich Himmler, the head of the SS, issued an order to SS units preparing to comb the Pripet Marshes in Belarus: "All male Jews must be shot. Drive the female Jews into the swamp." The SS officer in charge of the operation advised his superiors that "Driving women and children...