In June 1942, Thomas Mann, who was living in exile in California, delivered a commentary on a German-language BBC radio program that decried the sanguinary actions of the Third Reich in avenging the assassination of the leading SS official Reinhard Heydrich in Prague. After Heydrich’s elaborate funeral ceremony at the new Reich Chancellery in Berlin, Hitler screamed at the Czech president, Emil Hacha, “Nothing can prevent me from deporting millions of Czechs if they do not wish for peaceful coexistence.” It wasn’t an idle threat. “Since the violent death of Heydrich,” Mann lamented, “terror is raging everywhere, in a more...