History shows that the destruction of affluent societies is often self-induced. Why do once-successful societies ossify and decline? Hundreds of reasons have been adduced for the fall of Rome and the end of the Old Regime in 18th-century France. Reasons run from inflation and excessive spending to resource depletion and enemy invasion, when historians attempt to understand the sudden collapse of the Mycenaeans, the Aztecs, and, apparently, the modern Greeks. In literature from Catullus to Edward Gibbon, wealth and leisure — and who gets the most of both — more often than poverty and exhaustion, cause civilization to implode. One...