An important feature of Lenski's theory has been his emphasis on the need for a broadly inclusive approach in theory building. In a 1988 article, he argued that macrosociological theory should be based on our knowledge of the entire universe of human societies, past as well as present, and should seek to explain the major features of that universe, both its uniformities and its variations. This is undoubtedly a feature of the theory that many sociologists find troubling and unattractive because of the tradition developed in American sociology in the twentieth century of focusing theory and research on one's own society during a limited time period (i.e., American society in the 20th century) or a handful of societies (e.g., modern industrial societies) during an equally limited span of time.