This article argues that the democratic peace theorists have overlooked the defining development that underlies that peace of the nineteenth and twentieth centuries: the industrial-technological revolution. Not only did that revolution make democracy on a country scale possible; it also madeallthe countries that experienced the revolution—democratic and nondemocratic—far less belligerent in comparison with preindustrial times. The democratic peace did not exist among premodern democratic and republican city-states, not because they were not democratic or liberal enough but because they were premodern. Other factors that have emanated from the modern transformation and may generate greater aversion to war apply mostly to liberal democratic countries while being only variably connected to their regime. Such factors include the staggering rise in the standard of living; the decrease in hardship, pain, and death; the dominance of metropolitan life and the service economy; the spread of the consumer and entertainment society; sexual promiscuity; women's franchise; and the shrinking ratio of young males in the population.