United States v. McLean is a United States Supreme Court case that dealt with the issue of whether a federal court had the power to issue a writ of habeas corpus to a state court. The case involved a man named John McLean, who was convicted of murder in a state court in Tennessee. McLean sought a writ of habeas corpus from a federal court, claiming that his conviction was unconstitutional. 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 that was available only to federal courts, and that the federal court did not have the power to interfere with the decisions of a state court. The Court also noted that the writ of habeas corpus was a remedy that was available only in cases where the federal court had jurisdiction over the matter. The Court concluded that the federal court did not have jurisdiction over the matter, and thus could not issue a writ of habeas corpus.

In United States v. McLean, the Supreme Court was tasked with deciding whether or not a certain piece of land in California belonged to the federal government or to an individual who had purchased it from Mexico prior to its annexation by the United States. The majority opinion held that because this particular parcel of land had been part of Mexico at one point and then later became part of the United States, it was subject to U.S. laws and thus belonged to the federal government rather than any private individuals who may have previously owned it. Justice Field dissented from this decision, arguing that while he agreed with much of what his colleagues said about how Mexican law applied in such cases, he felt that there were other considerations which should be taken into account when determining ownership over disputed lands like these—namely, whether or not those claiming title could show evidence that they had actually acquired valid title under Mexican law before annexation occurred. In short, Justice Field argued for a more nuanced approach towards resolving disputes over contested lands between private individuals and governments so as not to unduly favor either side without due consideration being given for all relevant facts involved in each case