The outbreak of World War II on 1 September 1939, prompted Mann to offer anti-Nazi speeches (in German) to the German people via the BBC. In October 1940 he began monthly broadcasts, recorded in the U.S. and flown to London, where the BBC broadcast them to Germany on the longwave band. In these eight-minute addresses, Mann condemned Hitler and his "paladins" as crude philistines completely out of touch with European culture. In one noted speech he said, "The war is horrible, but it has the advantage of keeping Hitler from making speeches about culture." 
Mann was one of the few publicly active opponents of Nazism among German expatriates in the U.S. While some Germans claimed after the war that in his speeches he had endorsed the notion of collective guilt, others felt he had been highly critical also of the politically unstable Weimar Republic that preceded the Third Reich.