This uncertainty counts as one of the great triumphs of the modern age. In the past 70 years, supreme efforts have been made to erase national boundaries in Europe or at least render them harmless. This effort is known as the European Union, which includes 28 countries and, it must be said, is reliably boring. But that’s the whole idea. For thousands of years, the Continent generated not white papers but wars too numerous to mention—especially to Americans, who know them only from textbooks and strain to recall them only until the written test. “Europe’s Wars, 1648–1789: A Selection” takes up two pages in Appendix III of Norman Davies’ Europe: A History.