In the case of Rosebud Sioux Tribe v. Kneip, Governor of South Dakota et al., 1976, the U.S. Supreme Court ruled that Congress had effectively diminished the boundaries of the Rosebud Sioux Reservation in South Dakota through a series of statutes passed between 1904 and 1910. The tribe argued that these lands were unlawfully taken from them without their consent or compensation as required by treaty stipulations. However, based on an examination of legislative history and subsequent treatment of affected areas by federal officials, it was determined that Congress intended to diminish reservation boundaries with each successive statute opening portions for settlement by non-Indians. The court held that while unilateral congressional action could not terminate a reservation altogether (which would require tribal consent), it could change its boundaries; thus ruling against the tribe's claim to jurisdiction over those lands opened for settlement.

In the dissenting opinion for Rosebud Sioux Tribe v. Kneip, Justice Brennan argued that Congress did not clearly express its intent to diminish the boundaries of the Rosebud Reservation when it opened up parts of the reservation to non-Indian settlers in 1904 and 1910. He pointed out that previous Supreme Court decisions established a standard requiring clear congressional intent before tribal lands could be diminished or disestablished. In this case, he believed such clarity was lacking as there were no explicit references in either Act about diminishing or disestablishing reservation boundaries. Furthermore, he noted that historical context and subsequent treatment by federal officials suggested continued recognition of original reservation borders even after these Acts were passed. Therefore, according to Justice Brennan's interpretation, all unallotted lands within those original borders should still be considered part of the tribe’s territory under their jurisdiction.