society, they killed Jews, prostitutes, Romani people, and the mentally ill. On 31 July 1941, Hermann Göring gave written authorization to SS-Obergruppenführer (Senior Group Leader) Reinhard Heydrich, Chief of the Reich Security Main Office (RSHA), to prepare and submit a plan for a "total solution of the Jewish question" in territories under German control and to coordinate the participation of all involved government organisations. The resulting Generalplan Ost (General Plan for the East) called for deporting the population of occupied Eastern Europe and the Soviet Union to Siberia, for use as slave labour or to be murdered. The minutes of the Wannsee Conference estimated the Jewish population of the Soviet Union to be five million, including nearly three million in Ukraine. In addition to eliminating Jews, the Nazis also planned to reduce the population of the conquered territories by 30 million people through starvation in an action called the Hunger Plan devised by Herbert Backe. Food supplies would be diverted to the German army and German civilians. Cities would be razed and the land allowed to return to forest or resettled by German colonists. The objective of the Hunger Plan was to inflict deliberate mass starvation on the Slavic civilian populations under German occupation by directing all food supplies to the German home population and the Wehrmacht on the Eastern Front. According to the historian Timothy Snyder, "4.2 million Soviet citizens (largely Russians, Belarusians, and Ukrainians) were starved" by the Nazis (and the Nazi-controlled Wehrmacht) in 1941–1944 as a result of Backe's plan. Harvests were poor in Germany in 1940 and 1941 and food supplies were short, as large numbers of forced labourers had been brought into the country to work in the armaments industry. If these workers—as well as the German people—were to be adequately fed, there must be a sharp reduction in the number of "useless mouths", of whom the millions of Jews under German rule were, in the light of Nazi ideology, the most obvious example. At the time of the Wannsee Conference, the killing of Jews in the Soviet Union had already been underway for some months. Right from the start of Operation Barbarossa—the invasion of the Soviet Union—Einsatzgruppen were assigned to follow the army into the conquered areas and round up and kill Jews. In a letter dated 2 July 1941, Heydrich communicated to his SS and police leaders that the Einsatzgruppen were to execute