 It wasn't until the Oregon Trail began to be used by American settlers in the 1840s that British control of the Pacific Northwest, in the form of the Hudson's Bay Company, became challenged.Contact with Europeans and the frequent interaction between tribes accelerated the several epidemics that swept the region, beginning with smallpox in the 1770s and continuing with what was likely malaria in 1829, cholera in 1836, and smallpox again in 1853.The native population dropped from thousands to a few dozen.