In Evans v. Eaton, the Supreme Court of the United States held that a state court could not exercise jurisdiction over a federal officer acting in his official capacity. The case arose when an army paymaster was sued by one of his creditors for nonpayment on a debt incurred while he was stationed at Fort Smith, Arkansas Territory. The paymaster argued that as an agent of the United States government, he should be immune from suit in state courts and only subject to proceedings before federal tribunals or Congress itself. After considering both sides' arguments and relevant precedent, Chief Justice John Marshall concluded that since it is within Congress's power to create exclusive jurisdictions for certain matters involving its officers or agents, any attempt by states to interfere with those powers would be unconstitutional. As such, this decision established important principles regarding separation of powers between state and federal governments which remain applicable today.

In Evans v. Eaton, the Supreme Court was asked to decide whether a state court had jurisdiction over a case involving citizens of different states. The majority opinion held that it did not have such jurisdiction and dismissed the appeal. However, Justice Johnson dissented from this decision, arguing that the Constitution gave Congress exclusive power to regulate interstate commerce but did not give them authority to interfere with civil suits between individuals in different states. He argued further that if Congress could prevent such suits from being heard by state courts then they would be deprived of their right to access justice through those courts as guaranteed by Article III of the Constitution. Furthermore, he noted that allowing individual states to hear cases between citizens of other states would promote harmony among them and help protect rights regardless of where an individual resided or what their citizenship status may be.