Read this: Prior to 1871, the government of the United States regularly entered into treaties with Native Americans but the Indian Appropriations Act of March 3, 1871 (ch. 120, 16 Stat. 563) had a rider (25 U.S.C. § 71) attached that effectively ended the President’s treaty making by providing that no Indian nation or tribe shall be acknowledged as an independent nation, tribe, or power with whom the United States may contract by treaty. The federal government continued to provide similar contractual relations with the Indian tribes after 1871 by agreements, statutes, and executive orders.

A rider to the Indian Appropriations Act of 1871 provided that the US government could not do what with an Indian nation?
What is the answer? (If it cannot be answered, return "unanswerable")
contract by treaty