In these pages nearly seven years ago, Timothy Snyder asked the provocative question: Who killed more, Hitler or Stalin? As useful as that exercise in moral rigor was, some think the question itself might have been slightly off. Instead, it should have included a third tyrant of the 20th century, Chairman Mao. And not just that, but that Mao should have been the hands-down winner, with his ledger easily trumping the European dictators’.