For decades, scholars and politicians have marveled at the fact that democracies do not fight one another. “The absence of war between democracies comes as close as anything we have to an empirical law in international relations,” wrote the political scientist Jack Levy in 1988. “Democracies don't attack each other. They make better trading partners and partners in diplomacy,” U.S. President Bill Clinton declared in 1994. “There are no clear-cut cases of one democracy going to war against another,” the political scientist Michael Doyle wrote in 2024, “nor do any seem forthcoming.” The lack of war among the world’s many democracies is, indeed, impressive. But it is not the first time a group of like-minded countries have been at peace for an extended time period. From 1598 to 1894, most of East Asia—China, Japan, Korea, the Ryukyu Kingdom (now part of Japan), and Vietnam—was largely devoid of internal fighting.…