Pollard v. Lyon is a landmark United States Supreme Court case that established the principle of tribal sovereignty. The case involved a dispute between the Choctaw Nation and the state of Mississippi over the ownership of certain lands. The Choctaw Nation argued that the lands were part of their reservation and that the state had no authority to tax them. The state of Mississippi argued that the lands were not part of the reservation and that they had the right to tax them. The Supreme Court ruled in favor of the Choctaw Nation, holding that the lands were part of the reservation and that the state had no authority to tax them. The Court held that the Choctaw Nation was a sovereign nation and that the state of Mississippi had no authority to interfere with the Nation's internal affairs. The Court also held that the Choctaw Nation had the right to self-government and that the state of Mississippi had no authority to interfere with the Nation's internal affairs. The decision in Pollard v. Lyon established the principle of tribal sovereignty, which has been used to protect the rights of Native American tribes ever since. The decision also established the principle that the federal government has a duty to protect the rights of Native American tribes and to ensure that they are treated fairly.

In Pollard v. Lyon, the Supreme Court was asked to consider whether a state court had authority to issue an injunction preventing a party from prosecuting or defending any suit in another state. The majority opinion held that such an injunction was not within the power of the state court and therefore could not be enforced by it. However, Justice Field dissented on this point and argued that states have broad powers when it comes to protecting their citizens from harm caused by actions taken in other states. He reasoned that if a person's property is being threatened with seizure as part of litigation taking place outside of its jurisdiction, then it would be reasonable for the home state to take steps necessary for its protection - including issuing injunctions against further proceedings in foreign courts. Furthermore, he noted that while Congress has limited some aspects of judicial power between states through legislation like diversity jurisdiction statutes, there is no law which prevents one state from exercising its own authority over matters concerning itself and those who reside within its borders - even if they are involved with legal proceedings elsewhere.