Clark v. United States was a Supreme Court case that addressed the issue of whether a federal court had the power to issue a writ of habeas corpus to a state court. The case arose when a man named William Clark was convicted of murder in a state court in Virginia. He appealed his conviction to the Supreme Court of the United States, arguing that the state court had violated his constitutional rights. The Supreme Court held that the federal court did not have the power to issue a writ of habeas corpus to a state court. The Court reasoned that the writ of habeas corpus was a remedy available only to federal courts, and that the state court had the power to decide the case on its own merits. The Court also held that the state court had not violated Clark's constitutional rights, and that the conviction was valid. The decision in Clark v. United States established that federal courts do not have the power to issue writs of habeas corpus to state courts. This decision has been cited in numerous subsequent cases, and it remains an important precedent in the area of federal-state relations.

In Clark v. United States, the Supreme Court was asked to decide whether a federal court had jurisdiction over a case involving an alleged violation of state law. The majority opinion held that the federal courts did not have jurisdiction in this case because it involved only matters of state law and no matter of national concern. Justice Field dissented from this decision, arguing that Congress had given the federal courts authority to hear cases arising under both state and national laws as part of their duty to protect citizens' rights under the Constitution. He argued further that if Congress intended for such cases to be heard exclusively by state courts, they would have said so explicitly in legislation or other documents related to judicial power. Therefore, he concluded that since there was no explicit language denying federal court jurisdiction in these types of cases, then it should be assumed they do indeed possess such authority unless otherwise stated by Congress or another branch of government with constitutional powers over judicial proceedings.