What 'policy' did the ruling in Dred Scott v. Sandford put in place?

The U. S. Supreme Court hands down its decision on Sanford v. Dred Scott, a case that intensified national divisions over the issue of slavery.

In 1834, Dred Scott, a slave, had been taken to Illinois, a free state, and then Wisconsin territory, where the Missouri Compromise of 1820 prohibited slavery. Scott lived in Wisconsin with his master, Dr. John Emerson, for several years before returning to Missouri, a slave state. In 1846, after Emerson died, Scott sued his master’s widow for his freedom on the grounds that he had lived as a resident of a free state and territory. He won his suit in a lower court, but the Missouri supreme court reversed the decision. Scott appealed the decision, and as his new master, J. F. A. Sanford, was a resident of New York, a federal court decided to hear the case on the basis of the diversity of state citizenship represented. After a federal district court decided against Scott, the case came on appeal to the U. S. Supreme Court, which was divided along slavery and antislavery lines; although the Southern justices had a majority.

During the trial, the antislavery justices used the case to defend the constitutionality of the Missouri Compromise, which had been repealed by the Kansas-Nebraska Act of 1854. The Southern majority responded by ruling on March 6, 1857, that the Missouri Compromise was unconstitutional and that Congress had no power to prohibit slavery in the territories. Three of the Southern justices also held that African Americans who were slaves or whose ancestors were slaves were not entitled to the rights of a federal citizen and therefore had no standing in court. These rulings all confirmed that, in the view of the nation’s highest court, under no condition did Dred Scott have the legal right to request his freedom. The Supreme Court’s verdict further inflamed the irrepressible differences in America over the issue of slavery, which in 1861 erupted with the outbreak of the American Civil War.