On September 4, 1805, in the upper Bitterroot Valley of what is now western Montana, more than four hundred Salish people were encamped, pasturing horses, preparing for the fall bison hunt, and harvesting chokecherries as they had done for countless generations. As the Lewis and Clark expedition ventured into the territory of a sovereign Native nation, the Salish met the strangers with hospitality and vital provisions while receiving comparatively...