If anyone seemed to conform to Himmler’s aspirations for a Nordic elite, it was Heydrich. Himmler himself suffered from poor posture and a recessed chin, which he liked to hide in photos by covering it with his left hand. Heydrich represented everything Himmler was not — a tall blond with blue eyes who was a ladies’ man as well as a skilled sportsman, musician and pilot. Heydrich’s career as a naval officer ended abruptly because of an affair; his insolent conduct before a military court of honor resulted in his dismissal in 1931.

Heydrich was devastated. But his fiancée, Lina von Osten, was an ardent Nazi, and Heydrich’s family pulled some strings, landing him an interview with Himmler, who was impressed by Heydrich’s apparent familiarity with espionage, mostly gleaned from reading spy potboilers as a boy. According to Gerwarth, Heydrich had been largely apolitical and entered the most extreme paramilitary group within Hitler’s movement “not out of deep ideological conviction, but because Nazism offered him the opportunity to return to a structured life in uniform, providing along with it a sense of purpose and a way of regaining the confidence of Lina and her family of devoted Nazis.” Soon enough, however, Heydrich became one of the most zealous exponents of Nazi racial doctrine. Under Himmler’s guidance, Heydrich would play a key role in preparing the political and bureaucratic terrain on the road to Auschwitz.

When was the decision actually made to move from the extrusion of Jews from Germany and Western Europe to their actual liquidation? This question has vexed scholars for decades, leading to controversies between two schools of historians: the intentionalists, who believe Hitler was always determined to exterminate the Jews, and the functionalists, who contend that the Holocaust was arrived at in a rather haphazard fashion. The truth probably lies somewhere in between.

Hitler scarcely made a secret of his desire to wipe out the Jews: in 1939 he prophesied the extinction of world Jewry during a speech at the Kroll Opera House. And contrary to the notion derived from Hannah Arendt, most of the SS officials were not soulless technocrats — or as the German phrase has it, “desktop perpetrators” — but skillful bureaucrats driven by seething ideological hatreds. Himmler himself, Longerich writes, “liked to present himself in the pose of the victor” when visiting concentration camps and give “guided tours” of them. His eventual goal would have been to replace the Wehrmacht itself with his elite corps of Waffen-SS troops.

For all of Himmler’s zeal, however, the SS had to proceed carefully. It attracted much criticism, Longerich writes, from the Wehrmacht for engaging in flagrant atrocities during the 1939 invasion of Poland. Yet as Himmler saw it, the SS murdered “decently.” He distinguished between valid “political motives” for killing Jews and illegitimate “selfish, sadistic or sexual motives,” which would lead to prosecution for murder or manslaughter. It is important to remember that it was always Hitler who made the ultimate decisions in steadily moving toward a state-­sanctioned policy of extermination. According to Longerich, in 1941 “the initiative for the intensification of Jewish policy — in this case, the start of the deportations — once again came from Hitler, but Himmler, like other leading functionaries, intuited such a decision, felt his way forward and acted in advance of it and took on an active role as soon as the time was ripe.”

By 1942, the Nazis’ rapid military successes and anger over Heydrich’s death accelerated their plans to annihilate the Jews. Then, as defeat loomed, and in the wake of the failed assassination plot against Hitler on July 20, 1944, Himmler devoted himself to settling scores with the military and the Prussian aristocracy, who were often one and the same. The result was a fresh blood bath.

From the outset, Hitler and his fellow conspirators had been obsessed with the idea of avoiding a new November 1918, when they believed that internal Jewish and Communist subversives had stabbed imperial Germany in the back and cost it victory in World War I. And to the end, Hitler clung to the conviction that he was engaged in a titanic battle with world Jewry; in his final statement before he committed suicide, he called upon future generations to carry on the fight. Himmler himself committed suicide after he was captured by the British. Longerich and Gerwarth underscore that the Nazis’ sinister delusions about Jewish power prompted them to transform an entire continent into what Thomas Mann in his postwar novel “Doctor Faustus” called a “thick-walled torture chamber.”