One thing I think I’ve correctly observed about the U.S. military in the 21st century is that its leaders tend to be the last to want to go to war and the last to want to leave it. Political figures operate under public pressures and shifting geopolitical needs and goals; they’re surrounded by people who see the world a certain way; they get revved up, and say, “Go, invade.” Top military staff have reservations. They’ve studied the area, know the realities, the history—they have doctorates in it—and don’t want to get into anything America can’t win cleanly, decisively, relatively quickly....