The origin of the Upper Mississippian cultures is a matter of debate among archaeologists. They may have been local Late Woodland populations who were influenced by the large-scale chiefdom entities; or they may have originated in one of these more advanced societies and set out to “colonize” the marginal areas to the north. Aztalan is a site that represents an incursion of Middle Mississippians into Wisconsin; however, it is apparent that the Aztalan material culture is quite distinct from Upper Mississippian, so it does not necessarily follow that one evolved out of the other. There is evidence that from A.D. 1200-1500 there was a climatic cooling trend which appears to have made the growing system much less reliable in the Upper Mississippi area. This may have been why the culture “reverted” back to a smaller scale society with lesser dependence on agriculture for subsistence, and more emphasis on hunting and gathering.
