Americans keep dividing into two hostile camps. It seems the country is back to 1860 on the eve of the Civil War, rather than in 2018, during the greatest age of affluence, leisure and freedom in the history of civilization. The ancient historian Thucydides called the civil discord that tore apart the fifth century B.C. Greek city-states “stasis.” He saw stasis as a bitter civil war between the revolutionary masses and the traditionalist middle and upper classes. Something like that ancient divide is now infecting every aspect of American life. Americans increasingly are either proud of past U.S. traditions, ongoing...