President Obama observed this June that “if you had to choose any moment to be born in human history…you’d choose this time. The world is less violent than it has ever been.” While his proposition may seem incongruous with the present cavalcade of crises across Eurasia, the evidence suggests that the world is indeed becoming more secure. With Thanksgiving just behind us and the new year fast approaching, we should all give thanks. Consider nuclear dangers. During the Cuban Missile Crisis, which the late historian Arthur Schlesinger, Jr. famously called “the most dangerous moment in human history,” John F. Kennedy believed there was...