In 1914, shortly after he moved to Berlin to serve as director of the Kaiser Wilhelm Institute of Physics, Einstein was horrified by the onset of World War I. “Europe, in her insanity, has started something unbelievable,” he told a friend. “In such times one realizes to what a sad species of animal one belongs.” Writing to the French author Romain Rolland, he wondered whether “centuries of painstaking cultural effort” have “carried us no further than . . . the insanity of nationalism.”