The United States Supreme Court case of The United States v. Cruz Cervantes involved the interpretation of a treaty between Mexico and the United States, which was signed in 1848 at the end of the Mexican-American War. At issue was whether or not certain lands that were ceded to Mexico by Spain prior to 1821 could be considered part of Mexico when it became a republic in 1824. The court held that since these lands had been ceded before Mexico became an independent nation, they did not become part of its territory until after it declared independence from Spain and thus belonged to neither country under international law. This decision established an important precedent for determining ownership rights over disputed territories between nations with conflicting claims on them.

In the case of United States v. Cervantes, the Supreme Court was asked to decide whether a Mexican citizen who had been living in California since before it became part of the United States could be convicted for violating federal laws prohibiting certain types of firearms possession. The majority opinion held that Cervantes did not have any special rights as an alien and therefore could be prosecuted under federal law. However, Justice McLean dissented from this ruling on the grounds that Congress had no authority to pass such a law because it would violate both international treaties and state sovereignty over its own citizens. He argued that if Congress wanted to regulate firearm possession by aliens within U.S borders, then they should do so through diplomatic channels rather than criminalizing individuals like Cervantes who were already residing in California when it became part of America's territory.