According to the treaties that were never revoked it was never "ours" in the first place.
The Supreme Court ruled correctly in this case that half of Oklahoma is by treaty the property of the several native American tribes.
The whole issue of Native treaties is one too many non-Natives in both our countries either don't know about or try to downplay. It's also exactly why so many Natives are up in arms about things like pipelines and hydro dams-namely that their land rights are being stepped on.