POLITICAL STRESS IS at an all-time high. We are at pre–Civil War levels of animosity, according to Peter Turchin, an evolutionary anthropologist at the University of Connecticut, and Jack Goldstone, a sociologist at George Mason University, who study sources of unrest and political conflict. They developed a statistic—the political stress index—that incorporates income and wealth inequality, wage stagnation, national debt, competition between elites, distrust in government, social mobility, tax rates, urban density, demographics, and other factors that lead to instability and conflict.