In this vivid history of American western expansion, Conevery Bolton Valencius captures the excitement, romanticism, and confusion of the frontier experience as well as another, less renowned reality of settling: how terrifying the untamed wilderness of the West was to its homesteaders. In a time when good health was thought to involve perfectly balanced humors, settlers thought that the wild extremes of the borderlands disrupted the delicate equilibrium of their bodies. Valencius is the first historian to show that the settlers' primary criterion for uncharted land was its perceived health or sickliness. This is a beautifully written, fresh account of the gritty details of American expansion, animated by the voices of the settlers themselves.