In United States v. Gomez, the Supreme Court ruled that a person born in Mexico to Mexican parents was not an American citizen and could be deported from the United States without due process of law. The case involved Francisco Gomez, who had been living in California since 1851 but had never applied for naturalization or declared his intention to become a U.S. citizen as required by law at the time. When he was arrested for vagrancy and threatened with deportation, he argued that he should have been granted due process before being removed from the country because he was an American citizen by birthright under existing laws governing citizenship status of persons born abroad to foreign-born parents. However, the Supreme Court held that those laws did not apply in this case because they only applied to persons born outside of America whose fathers were citizens at their birth; since neither parent of Francisco Gomez was a U.S.-citizen when Francisco himself was born, these laws did not protect him against deportation without due process rights being afforded him first

In United States v. Gomez, 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 tried for murder under federal law. The majority opinion held that he could not because he was not subject to U.S. jurisdiction at the time of his alleged crime and thus did not fall within Congress's power to define and punish crimes committed against its laws or citizens abroad. In dissent, Justice Field argued that Congress has broad authority over all persons residing in territories acquired by the United States regardless of their citizenship status, including those who were present prior to acquisition such as Gomez. He further argued that even if this were not true, there is no doubt that when a territory becomes part of the Union its inhabitants become subject to national laws and can be prosecuted accordingly for any offenses they commit therein after annexation takes place—which is exactly what happened here with respect to Gomez's case