Case v. Brown was a Supreme Court case that dealt with the issue of slavery and emancipation in the United States. The plaintiff, William Case, had purchased a slave named Mary Ann Brown from her owner in 1859. After purchasing her, he moved to Ohio where slavery was illegal under state law. In 1862, Mary Ann sued for freedom on the grounds that she had been illegally held as a slave since moving to Ohio two years prior. The Supreme Court ultimately ruled in favor of Mary Ann Brown and declared that she should be emancipated immediately due to the fact that it was illegal for slaves to be held within Ohio's borders at any time during their residence there. This ruling set an important precedent regarding how states could handle cases involving slavery and emancipation going forward; it also established legal protection for those who were unlawfully enslaved while residing within free states or territories across America.

In the case of Case v. Brown, the Supreme Court was asked to decide whether a state statute that prohibited African Americans from testifying against white people in court was constitutional. The majority opinion held that it did not violate any federal laws and thus could stand as valid law within the state. However, Justice Field dissented from this ruling on two grounds: firstly, he argued that such a law violated both the Thirteenth Amendment's prohibition on slavery and involuntary servitude and secondly, he believed it violated Article IV of the Constitution which guarantees citizens "the Privileges or Immunities of Citizens in several States." He further noted that if states were allowed to pass laws like this one then they would be able to effectively deny African Americans their right to testify in court altogether - an action which would render them unable to protect themselves legally when wronged by whites. In conclusion, Justice Field argued strongly for overturning this decision due its clear violation of fundamental rights guaranteed by both federal statutes and constitutional amendments.