Just spitballing here, but maybe "Indian removal" is handled differently and all Amerindian tribes are considered one people by the policymakers, concentrating their population into or around a single settlement in a western territory. Maybe by force? Like a limited, temporary, and less severe internment?
When the internment period is over, the second generation natives just stay and are treated well by local non-natives. The town grows. When western expansion heats up, freemen and white settlers bolster the population (maybe it's a river town between Fort Coffee, OK and Fort Smith, AR?) and other displaced natives hear stories of how Native peoples are treated there after they are left alon and migrate.
It's a cool idea, as a large Chicago, Memphis, or St. Louis type city with that many different tribes will have similar issues to Italian and Irish groups in cities east of the Mississippi. A lot of inter-tribal alliances and strive in the streets (think gangs of New York meets Last of the Mohicans...)
Native American organized crime movies would be... well incredibly awesome.
What would they name a place like that?