While the dispossession of Native peoples began well before the founding of the United States, the federal government formalized and accelerated the forced removal of Indigenous people from their ancestral lands in the nineteenth century. That displacement — often the result of armed conflict or coerced treaties — enabled the United States’ conquest of vast acres of Tribal territory. The expansion was guided by the idea of “Manifest Destiny” — the belief that the United States’ territorial expansion westward was both inevitable and morally justifiable because white American settlers had a providential mission to control and transform the continent.

The completion of the Transcontinental Railroad in 1869 accelerated western settlement in new ways, enabling the incorporation of new territories into the national market economy. Waves of recently-arrived immigrants moved west and corporations soon followed, seizing opportunities the railroads created. In 1893, historian Frederick Jackson Turner, in his famous address to the American Historical Association, proclaimed that the frontier had closed.