Some early models of societal evolution emphasized intersocietal relations as a critical force in the evolution of any give society. Yet, with but a few exceptions, the unit of evolutionary analysis remained the individual society. Beginning in the 1960s, models of intersocietal relations—particularly geoeconomic and geopolitical—began to emphasize the system of societies as a critical unit of analysis. The evolution of any particular society has been increasingly viewed as a result of the dynamic evolution of the systems of societies that have emerged at all points in human history, and particularly the global economic system that has emerged over the last few hundred years. Often termed “world systems analysis,” this new interpretation of societal evolution has, to some degree, replaced the older stage models, even those developed in the modern era, of societal evolution. Intersocietal analysis is thus one of the most prominent forms of evolutionary theorizing and research in sociology and some of the other social sciences.