Native American reservations

Native American reservations are partitions of land allocated to the native people of the United States of America, spread across the entirety of the country.

Background
As the United States continued to spread westward from the coast, more and more of the Native Americans were forced off of their land. Eventually, these people would be given legal designations of land to live on known as reservations, which were overseen by a branch of the federal government.

When the bombs fell and the government collapsed, there was no longer anyone to keep them from expanding and claiming more land. Bands of people left, heading into the Wasteland and going on to join various factions. Starting in 2095, multiple groups encountered and joined the Blackfoot tribe.

Another from a place known as Res, likely the Navajo Nation, joined the Dead Horses. Many of these tribes would later be wiped out or assimilated by Caesar's Legion.

Appearances
Native American reservations are mentioned in the Fallout: New Vegas add-on Honest Hearts and the design documents for Black Isle Studios' cancelled Fallout 3.