From “Undoing Manifest Destiny: Settler America, Christian Colonists, and the Pursuit of Justice” by L. Daniel Hawk
Treaty making became the preeminent means of getting Indian land until 1871, when Congress dispensed with the practice. Virtually all treaties the United States made with Indigenous bodies required land cessions as the price necessary to end hostilities or to avert threatened violence. Nevertheless, purchasing land by treaty reinforced the fiction, among settler elites, that the United States acquired the land fairly, honorably, and legally. Adding to the fiction was the settler conviction that the terms the United States dedicated were more than generous. The settler nation, after all, already owned the land, having acquired title from Great Britain. The United States, in settler minds, was thus paying the Indians for land that they, the settler nation, already owned.
The perceived generosity of the treaty terms, however, paled in comparison to the magnanimous gift the settler nation believed it gave to Indigenous peoples, namely, the opportunity to enjoy the benefits of their civilization. In settler thinking, the gift of civilization more than compensated Indians for the loss of their land. If Indians rejected the gift and refused to relinquish their land, the fault for the consequences lay with them.