Earlier quoted context omitted.
These rights existing because the US government signed treaties with independent foreign nations. Those treaties are valid law until the Congress withdraws from them.
Did the US government ever acknowledge them as independent foreign nations? The War of Independence was partly fought to get away from the British proclamation of 1763 that said you couldn't settle west of the Appalachians without a treaty. Oklahoma was part of the Louisiana purchase, the US considered it their land for that reason. The US signed treaties with the indigeneous population in an attempt to secure peace,…
and by doing so, acknowledged that those indigenous populations were soveriegn nations. It doesn't matter why they signed those treaties, the only thing that matters is that they did.
You don't get to cancel a treaty just because the other party used to have leverage over you and doesn't anymore.