In Masters of Death, Pulitzer Prize-winning author Rhodes gives full weight, for the first time, to the Einsatzgruppen's role in the Holocaust. These "special task forces," organized by Heinrich Himmler to follow the German army as it advanced into eastern Poland and Russia, were the agents of the first phase of the Final Solution. They murdered more than 1.5 million men, women, and children between 1941 and 1943, often by shooting them into killing pits, as at Babi Yar.

These massive crimes have been generally overlooked or underestimated by Holocaust historians, who have...