Even a small war is hellish for those caught up in it, of course. But a world war is the worst thing we humans have ever done to one another. In a memorable essay published last month, Henry Kissinger reflected on “How to Avoid Another World War.” In 1914, “The nations of Europe, insufficiently familiar with how technology had enhanced their respective military forces, proceeded to inflict unprecedented devastation on one another.” Then, after two years of industrialized slaughter, “the principal combatants in the West (Britain, France and Germany) began to explore prospects for ending the carnage.” Even with US intermediation, the effort failed.