Sanders completed his doctoral dissertation,
Tierra y Agua: a Study of Ecological Factors in the Development and Personality of Mesoamerican Civilizations after taking up a post as an assistant professor at the
University of Mississippi in 1956, subsequently moving to
Penn State University, where he spent the rest of his academic career, three years later and becoming an associate professor in 1962. He undertook a survey of
Teotihuacan from 1960 to 1964, the results of which were published in the 1965 book
The Cultural Ecology of the Teotihuacan Valley. He was named a professor in 1966. He subsequently shifted his attention southward to
Kaminaljuyu in
Guatemala, in part due to evidence of links between that
Mayan site and Teotihuacan. In 1979,
The Basin of Mexico: Ecological Processes in the Evolution of a Civilization, a regional analysis synthesising multiple survey results spanning 3000 years which was co-authored by Sanders, was published: due to its bright green cover and influence, it has been nicknamed "The Green Bible". During the 1980s and 1990s he co-directed survey work at the Classic Maya site of
Copán in
Honduras. In 1985, he was elected to the
National Academy of Sciences. Outside of the U.S., he also served as a visiting professor at the
Instituto Nacional de Antropología e Historia, the
National Autonomous University of Mexico and the National School of Anthropology and History in Mexico. Sanders' approach was influenced by cultural evolutionism, and laid particular stress on
cultural ecology, emphasising the relationship between people and their surroundings, and seeking similarities in different cultures in their response to specific environmental conditions. As such, he saw the study of settlement patters in a society as key, and bound up the study of ecological and demographic developments. During his studies at Harvard, he developed the concept of the "central Mexican symbiotic region", referring to the network of symbiotic and mutually beneficial social and economic relationships that existed across a diversity of ecological zones in central Mexico prior to the
Spanish conquest of the Aztec Empire. He argued that this area saw earlier and more acute urban development and state formation than other areas of Mexico, which he believed was the result of its physical geography: a semiarid climate which facilitated land clearance, variations in altitude meaning that it contained conditions suitable for growing maize, cotton and agave, and unpredictable levels of rainfall which spurred the development of irrigation and intensive agriculture. This in turn led to high population densities which could support more sophisticated agricultural techniques ==Death==