Mahmood Mamdani in Lapham’s Quarterly:
In the early period of American colonization, there was no reference to a place called Indian country. That is because every place was Indian country. Settlers in Maine rented land from Indians. In the Dutch and English colonies, settlers purchased land from Indians, either wholesale or piecemeal.
The term Indian country was first used in King George III’s Royal Proclamation of 1763. Under the system delineated by the Crown, Indian country was territory that Indians had the right to use but over which they did not have domain. The Crown retained the title to all colonized lands occupied by Indian tribes and granted the tribes use rights, which the king could revoke at will. Because the land belonged to the Crown, Indians who wished to sell their use rights could sell only to the Crown. After the War of Independence, the United States adopted the same scheme, and to this day Indians on reservations retain only “Indian title” or “right of occupancy.” Their holdings can be dissolved by congressional action.
The original language of the Constitution makes clear that Indians are aliens in the United States. The document makes just one substantive reference to Indians. In article 1, section 8, Congress is granted power “to regulate commerce with foreign nations and among the several states, and with Indian Tribes.” Leading theorists of the early republic also understood the Indians as a foreign challenger to settlement. In Federalist 24 Alexander Hamilton described “the savage tribes on our western frontier” as natural enemies of the United States and natural allies of the British and Spanish, and he cited Indian tribes as justification for maintaining a national defense force. In Federalist 25 Hamilton reiterated his view that Indians were foreign enemies, raising the specter that Britain and Spain would join forces with Indian tribes to encircle the union from Maine to Georgia. Later arguments for the Second Amendment right to form armed militias for collective defense of the “free state” are easily understood from the perspective of settlers who feared attacks by natives perceived to be enemies of that state.
The view of Indian tribes as enemies and aliens had to be squared with the undeniable fact that Indians lived in territories claimed by the nascent United States.
More here.