What Drives Societal Collapse?

The archeological and historical record is replete with evidence for prehistoric, ancient and pre-modern societal collapse. These collapses occurred quite suddenly and frequently involved regional abandonment, replacement of one subsistence base by another (such as agriculture by pastoralism) or conversion to a lower energy socio-political organization (such as local state from interregional empire). Each of these collapse episodes has been discussed intensively within the archeological community, commonly leading to the conclusion that combinations of social, political, and economic factors were their root causes. That perspective is now changing with the accumulation of high-resolution paleoclimatic data that provide an independent measure of the timing, amplitude and duration of past climate events. These climatic events were abrupt, involved new conditions that were unfamiliar to the inhabitants of the time, and persisted for decades to centuries. They were therefore highly disruptive, leading to societal collapse-- an adaptive response to otherwise insurmountable stresses (1). In the Old World, the earliest well-documented example of societal collapse is