The Crow Indians lived on a reservation in Montana. The federal treaty provided that the Crow Indians retained hunting and fishing privileges on the reservation. Beginning in the 1920s, the reservation was divided into private parcels pursuant to the Crow Allotment Act, 41 Stat. 751. Individual lots were sold to both Indians and non-Indians. The Crow Indians enacted a resolution that prohibited all non-Indians from fishing or hunting on the reservation, whether or not the non-Indians owned land in fee simple. The State of Montana (defendant) continued to enforce hunting and fishing regulations against non-Indians who lived on the reservation. The United States (plaintiff) sued on behalf of the Crow Indians, seeking declaratory judgment that the Crow Indians and the United States had exclusive authority to regulate hunting and fishing on the reservation. The district court denied relief, holding that because the Crow Indians were not authorized by treaty or law to regulate the hunting and fishing of non-Indians on the reservation, it was proper for Montana to regulate these matters. The ninth circuit reversed. The court held that the Crow Indians were authorized by both treaty and inherent sovereignty to regulate—but not to prohibit—the fishing and hunting activities of non-Indian fee owners on the reservation. The United States Supreme Court granted certiorari.