The United States Supreme Court case of The United States v. Alexis Porche concerned the issue of whether a slave who had been brought to Louisiana from Cuba was free or not. The court held that under the terms of the Treaty between Spain and France, which ceded Louisiana to France in 1800, all slaves then present in Louisiana were emancipated by virtue of their presence there. As such, it was determined that Alexis Porche should be set free as he had been brought into Louisiana after this date and thus fell within the scope of emancipation provided for by said treaty. This decision marked an important step forward in recognizing freedom for African Americans living in America at this time and further established precedent regarding how treaties could impact existing laws concerning slavery.

In the case of United States v. Alexis Porche, the Supreme Court was tasked with determining whether a slave who had been brought to New York by his master and subsequently emancipated could be considered a citizen of that state. The majority opinion held that since slavery was not recognized in New York, Porche should be considered a citizen; however, Justice McLean dissented from this decision. He argued that while it is true that slaves are no longer subject to their masters' control once they enter into free states or territories, they do not necessarily become citizens as well. According to McLean's dissent, citizenship requires more than just freedom from bondage—it also requires an individual's consent and allegiance to the laws of the state in which he resides. As such, he concluded that Porche did not meet these requirements and thus could not be considered a citizen of New York State despite being freed from slavery there.