“Power changes people, and it changes nations,” Robert Kagan says in his slim, insightful guide to contemporary politics. In a little more than a 100 pages, Kagan explores the upcoming competition of the U.S. and China (maybe a war), the frustration of radical Islamists to turn back the clock of modernity 1,400 years, and the surety that terrorists will acquire and use nuclear weapons. In a couple of hours, Kagan can reorient your geopolitical vision.