It’s a good time to be a pessimist. ISIS, Crimea, Donetsk, Gaza, Burma, Ebola, school shootings, campus rapes, wife-beating athletes, lethal cops—who can avoid the feeling that things fall apart, the center cannot hold? Last year Martin Dempsey, chairman of the Joint Chiefs of Staff, testified before a Senate committee that the world is “more dangerous than it has ever been.” This past...