The susceptibility of the Canadian plains to drought is widely considered the greatest threat to the economic and social stability of the region. Rather than simply a condition of the physical environment, vulnerability to drought is a cultural phenomenon with its origins in the spread of the modern world system to the northern Great Plains. This point is illustrated by the relationship of indigenous societies to the region in the late prehistoric period. For hundreds of years after the climatic downturn of the 13th century, the grasslands served as a refuge for many groups experiencing climatically driven hardship in other regions, even though the country was more prone to desiccation than at any time in the recent past. Two key subsistence strategies that were used in the region were pedestrian bison hunting and the management of water through the proscription of beaver hunting. As market forces took hold, these ancient and effective practices were lost, contributing to climatic vulnerability, violence and ultimately to the end of the bison economy.