The United States v. Zephaniah Kingsley was a Supreme Court case that addressed the issue of slavery and freedom in America. The case centered around Zephaniah Kingsley, an African American man who had been born into slavery but later purchased his own freedom from his former master. After purchasing his freedom, he married a woman who was also formerly enslaved and moved to Florida with her and their children. In 1837, they were arrested by federal authorities for violating the laws prohibiting interracial marriage between whites and non-whites in some states at that time. The US Supreme Court ultimately ruled in favor of Kingsley's right to marry whomever he chose regardless of race or color as well as affirmed the validity of contracts made between slaves prior to emancipation such as those related to buying one's own freedom from enslavement. This ruling set an important precedent regarding individual rights within the context of slavery which would be further expanded upon over subsequent decades leading up to its eventual abolishment throughout America during 1865-1870s Reconstruction period following the Civil War

In the case of The United States v. Zephaniah Kingsley, Justice McLean wrote a dissenting opinion in which he argued that Congress had no authority to pass laws regarding slavery and emancipation within the state of Florida. He stated that while Congress did have power over territories acquired from foreign nations, it was not granted any such power by the Constitution with regard to states already existing at its adoption. Furthermore, he claimed that if Congress were allowed to interfere with matters concerning slavery or emancipation in individual states then this would be an unconstitutional exercise of federal authority over state sovereignty. In conclusion, Justice McLean asserted that as long as there is no express constitutional provision granting such powers to Congress then they cannot legally regulate these issues within individual states without infringing upon their rights under the Tenth Amendment.