In United States v. D'Aguirre, the Supreme Court considered a case involving an alleged violation of the Neutrality Act of 1794. The defendant was accused of attempting to enlist men in Louisiana for service in a foreign war against Spain without obtaining permission from Congress as required by law. The court held that although there were no specific penalties provided for violations of this act, it was still enforceable and punishable under general criminal laws prohibiting treason or other offenses against the government. Furthermore, they found that since Congress had not repealed or modified any part of the neutrality statute, it remained valid and binding on all citizens regardless if they knew about its existence or not. Ultimately, the court concluded that D'Aguirre's actions constituted a crime and he could be punished accordingly.

In United States v. D'Aguirre, the Supreme Court was asked to decide whether a person who had been born in Mexico and later moved to California could be considered a citizen of the United States. The majority opinion held that such an individual did not qualify as a citizen under existing law, but Justice Field dissented from this decision. He argued that since the Mexican-American War had ended with Mexico ceding its territories to the US, anyone living in those territories at that time should have automatically become citizens of the US without any further action on their part or recognition by Congress. Furthermore, he noted that many individuals who were born in foreign countries and then moved to America would otherwise be denied citizenship due to their lack of formal naturalization proceedings; thus denying them basic rights enjoyed by other citizens such as voting and owning property. In conclusion, Justice Field believed it was unjust for these people not to receive full citizenship status simply because they were born outside of American borders prior to becoming residents within them.