They are like any other foreign power in that respect. The United States could make a treaty with Spain and cede territory. The United States could break that treaty. The United States could declare war with Mexico and take the Southwest.
Except there’s this:
1. Federal Trust Relationship: The federal government has a trust responsibility to protect tribal sovereignty and interests. This relationship implies that the government must act in the best interests of tribes, providing a legal framework for their rights and governance.
2. Supreme Court Interpretations: Over the years, the Supreme Court has developed a body of law that defines the status of Indian tribes within the federal system. This includes recognizing tribes as distinct sovereign entities that operate within a limited sphere, separate from state and federal governments.