In this narrative history of the Einsatzgruppen--killer task forces deployed in Poland and the Soviet Union early in World War II by Himmler's SS--Richard Rhodes argues that Hitler made two separate decisions to murder the Jews of Europe. The first, in July 1941, condemned the eastern European Jews to slaughter by the Einsatzgruppen, who would execute 1.5 million victims between 1941 and 1943 by shooting them into killing pits, as at Babi Yar--crimes against humanity that have largely been overlooked or underemphasized by Holocaust historians. The second decision, in December 1941, condemned the Jews of western Europe. By then, Rhodes shows, direct killing had so brutalized the SS perpetrators that a shocked Himmler had ordered the development of less personal means of murder--the notorious gas chambers and crematoriums of the Holocaust's second wave. Rhodes demonstrates further that Hitler and Himmler intended the Jews to be only their first victims; their plan was to open up Russia to German colonization, and to destroy more than 30 million Slavs and members of other ethnic groups. Drawing on newly available material, this is a book that is certain to generate debate, and expand the understanding of the Holocaust.