This ^^ huge portions of land are owned by the current federal US government that could be easily ceeded. Lands that are owned by first nations can still have white people in them, as citizens of those nations, we aren't building ethnostates. It's also not like first people will demand the destruction of existing infrastructure, what's more, because of climate change we will need to have mass movement / transplantation of people away from the coasts and the equator. We can use this opportunity to rip out the roots of settler kkklonialism. People are gonna have to move anyways.