In United States v. Armejo, the Supreme Court of the United States was tasked with determining whether a Mexican citizen who had been living in California since 1848 could be convicted under an 1862 act that made it illegal for any person not a naturalized citizen to possess firearms within U.S. territory without permission from Congress or other authorized authority. The court held that although Armejo had resided in California since before its admission into the Union as a state, he was still subject to federal law and thus liable for his violation of said law due to his lack of citizenship status at the time of arrest and conviction. Furthermore, they noted that even if he were considered a "resident" rather than merely present on U.S soil, this would not exempt him from criminal liability because such residency did not confer upon him any special privileges or immunities beyond those granted by Congress through naturalization laws and treaties with foreign nations like Mexico which allowed certain individuals born abroad to become citizens after residing in America for some period of time

In United States v. Armejo, the Supreme Court was asked to decide whether a Mexican citizen who had been living in California since 1848 and became a naturalized American citizen in 1860 could be convicted of treason against the United States for joining an armed rebellion against it. The majority opinion held that he could not because his allegiance shifted from Mexico to the U.S., so he was no longer subject to prosecution under Mexican law or liable for any acts committed before becoming a U.S. citizen; however, Justice Field dissented on this point and argued that although Armejo had become an American citizen, his prior allegiance still made him liable for any treasonable acts committed while owing loyalty to Mexico—even if those actions occurred after he became an American citizen but before Congress declared war on Mexico in 1861. He further contended that even though Armejo's citizenship status changed when he took the oath of allegiance, it did not absolve him from responsibility for past offenses as long as they were committed during his period of foreign service or while owing fealty elsewhere than America