Dred Scott v. Sandford was a landmark decision of the United States Supreme Court that held the U.S. Constitution did not extend American citizenship to people of black African descent, and thus they could not enjoy the rights and privileges the Constitution conferred upon American citizens.^[69] The Supreme Court's decision has been widely denounced, both for its overt racism and for its crucial role in the start of the American Civil War four years later.^[70] Legal scholar Bernard Schwartz said that it "stands first in any list of the worst Supreme Court decisions". Chief Justice Charles Evans Hughes called it the Court's "greatest self-inflicted wound".^[71]

The decision involved the case of Dred Scott, an enslaved black man whose owners had taken him from Missouri, a slave-holding state, into Illinois and the Wisconsin Territory, where slavery was illegal. When his owners later brought him back to Missouri, Scott sued for his freedom and claimed that because he had been taken into "free" U.S. territory, he had automatically been freed and was legally no longer a slave. Scott sued first in Missouri state court, which ruled that he was still a slave under its law. He then sued in U.S. federal court, which ruled against him by deciding that it had to apply Missouri law to the case. He then appealed to the U.S. Supreme Court.

In March 1857, the Supreme Court issued a 7–2 decision against Scott. In an opinion written by Chief Justice Roger Taney, the Court ruled that people of African descent "are not included, and were not intended to be included, under the word 'citizens' in the Constitution, and can therefore claim none of the rights and privileges which that instrument provides for and secures to citizens of the United States". Taney supported his ruling with an extended survey of American state and local laws from the time of the Constitution's drafting in 1787 that purported to show that a "perpetual and impassable barrier was intended to be erected between the white race and the one which they had reduced to slavery". Because the Court ruled that Scott was not an American citizen, he was also not a citizen of any state and, accordingly, could never establish the "diversity of citizenship" that Article III of the U.S. Constitution requires for a U.S. federal court to be able to exercise jurisdiction over a case. After ruling on those issues surrounding Scott, Taney struck down the Missouri Compromise as a limitation on slave owners' property rights that exceeded the U.S. Congress's constitutional powers.