… the U.S. Supreme Court handed down the Dred Scott decision.
[Chief Justice] Taney’s “Opinion of the Court” stated that Negroes were not citizens of the United States and had no right to bring suit in a federal court. In addition, Dred Scott had not become a free man as a result of his residence at Fort Snelling because the Missouri Compromise was unconstitutional; Congress had no authority to prohibit slavery in the federal territories. . . . Because Dred Scott was not free under either the provisions of the Northwest Ordinance of 1787 or the 1820 Missouri Compromise, he was still a slave, not a citizen with the right to bring suit in the federal court system. According to Taney’s opinion, African Americans were “beings of an inferior order so far inferior, that they had no rights which the white man was bound to respect.” . . . Taney returned the case to the circuit court with instructions to dismiss it for want of jurisdiction.
Above from the Missouri State Archives, which has an extensive report on the case.
Scott and his wife Harriet, also a party to the case, were freed shortly after by their new owner, but Dred Scott died the following year and his wife and daughter not much later.
Before the ruling, many of those moderately opposed to slavery felt the institution would die out soon enough if it wasn’t allowed to expand. The 7-2 decision of the Court seriously undermined the effort to limit the expansion, however; indeed, some feared that under its precedent even the free states would soon be unable to outlaw slavery. The Scott decision eliminated the middle ground in the debate.