In 1625 the British philosopher Francis Bacon defined vengeance as “a kind of wild justice.” “The more man’s nature runs to [vengeance],” he wrote, “the more ought law to weed it out.” But some types of vengeance were more acceptable than others, and Bacon clarified that “the most tolerable sort of revenge is for those wrongs which there is no law to remedy.” Though World War II’s industrialized brutality would have been unimaginable to Bacon, and is still unimaginable to us nearly a century later, Nazi Germany’s genocidal march across Europe surely falls into the category of “those wrongs which...