In "The Third Wave", Toffler describes three types of societies, based on the concept of "waves"—each wave pushes the older societies and cultures aside. He describes the "First Wave" as the society after agrarian revolution and replaced the first hunter-gatherer cultures. The "Second Wave," he labels society during the Industrial Revolution (ca. late 17th century through the mid-20th century). That period saw the increase of urban industrial populations which had undermined the traditional nuclear family, and initiated a factory-like education system, and the growth of the corporation. Toffler said: