If legal scholars are not in agreement about the meaning of Crow Dog, the same cannot be said for United States v. Kagama. This case, decided on May 10, 1886, is known as the Supreme Court's first statement of the plenary power doctrine, the principle that Congress's power over Indian affairs is unlimited by treaty rights or tribal sovereignty. As one of the most important cases in federal Indian law, Kagama stands for principles opposite those advanced in Crow Dog and Worcester. Kagama left Indian tribes mere “wards” of the federal government, totally dependent on the will of Congress, which could assert its political power even to their termination as tribes and the expropriation of their lands without compensation. Kagama is the judicial embodiment of Congress's policy of forcing the assimilation of the tribes, recognizing none of their sovereignty, none of their status as domestic nations.

Kagama and Crow Dog are closely linked, not only as products of the same Court, a little more than two years apart, but also doctrinally in that Kagama represents the judicial approval of the Major Crimes Act, the congressional restriction of the sovereignty of tribal law that the Court had recognized in Crow Dog. The Court itself in Crow Dog specifically stated that Congress had the power to extend federal criminal law in Indian country if it chose to do so, citing congressional extension of federal liquor laws to Indian country without the consent of the tribes in United States v Forty-three Gallons of Whiskey (1876)..