The 18th century marked a time of unprecedented changes in indigenous adaptation patterns to climatic variability in the SSRB. European influences usurped climactic stimuli as the pre-eminent cause of material and cultural change in the region. Inhabitants of the region had to contend with new challenges arising from the fur trade economy and found themselves increasingly vulnerable to the effects of negative climatic stimuli. The four-hundred year pattern of westward migration by woodland peoples into the SSRB dramatically accelerated as they moved to meet the demands created by the fur trade. Additionally, in the mid-1700s, the introduction of the horse led to an equestrian dependency that further compromised the security of groups to the climatic variability. Differential access to horses and European goods, particularly firearms, affected the balance of power in the SSRB and contributed to the forcible displacement of some groups. Finally, in the 1780s, a devastating epidemic struck the plains with such ferocity that some groups ceased to exist as distinct entities; leading to the emergence of new equestrian communities. The fragility of horse populations in the face of unpredictable harsh weather patterns at the end of the 18th century highlighted the increased susceptibility of Basin peoples to negative climactic stimuli. Herd depletion limited the ability of various groups to participate in the commercially driven bison hunt. Afflicted parties sought to replenish their herds by engaging in opportunistic raids upon adjacent populations. The ensuing warfare over horses, territory, and status within the fur trade further endangered the ability of all groups in the region to survive extreme climactic episodes. Once aboriginal societies in the SSRB began making adaptations to accommodate the European-controlled fur trade economy, they ceased employing and refining those coping strategies which had previously buffered Basin occupants from destructive climatic stimuli.