The European settlers in the Americas were regularly attacking each other for land, ports, etc. (French & British, British & Dutch, Colonists/Americans & Canadians & British, Americans vs. Mexico, Nicaragua (Walker), Cuba, etc.) while the tribes were in a state of continual warfare with nearly all of their neighboring tribes with endless invasions, mass migrations, and incursions (the Iroquois Confederacy or Powhatan's Tidewater Confederacy are both rare but impressive as to what could be accomplished.)
If the POD was in the 1200's with the Mississipian Civilization not collapsing throughout what would be the Louisiana Territory but instead continuing to grow and progress while getting through European diseases better from the 1500's Spanish expeditions, there'd be several million organized people in cities with standing armies that had traded for some European arms (armor and swords of copper are found in the mound burials routinely so clearly it's mostly gunpowder weapons they'd lack and trading with the French, Spanish, Dutch, etc. just an in OTL's 18th & 19th Centuries could make up for a lot of the difference.
POD 1780 when policies towards Indian lands, tribal negotiations, treaties, raid retaliation, etc. were pretty well set over 180 years (Roanoke forward) would be very tough as noted. The diseases wiped out the civilized tribes in organized populations most likely to assimilate and negotiate (like the Cherokee, Iroquois, Creek, Ojibwe, Osage, Crow/Hidatsa, Mandan, etc.) so making those far less lethal would drastically change the possibilities. Most of these lived in complex civil societies with permanent farm land that was considerably more productive and used crops they'd developed themselves while participating in vast trade networks. The roaming nomadic bands are rarer than portrayed and probably reflect epidemic survivors from the large Indian settlements, dispersal and annual contact (sun dance in June equinox) working like quarantines.
Your POD could work with U.S. Constitutional protections for the American Indians like full citizenship as part of treaties, voting rights, creating reservations as regular county governments operating within the common hierarchy instead of a weird separate status, much better defined land titles/land purchase systems with actual enforcement (private real estate developers/distant land speculators bear a lot of the guilt for what happened but get let off the hook as though official actions are all that impact this.) I think Benjamin Franklin did want to do a lot more for the Indians from his own negotiations with them on Pennsylvania's borderlands so having James Madison (Bill of Rights, most of the Constitution), Washington, Alexander Hamilton (NYC's top real estate lawyer as well as Secretary of the Treasury and big proponent of national infrastructure investment like roads into the frontiers), Aaron Burr (NYC's other top real estate lawyer), etc. come around to this way of thinking during the Constitutional Congress and early years under the first 5 Presidents you might get there.