Final answer:
In the Dred Scott v. Sandford case of 1857, the Supreme Court ruled that Dred Scott remained enslaved, Black people could not be U.S. citizens, and Congress had no power to ban slavery in U.S. territories.
Step-by-step explanation:
The Supreme Court decided an important slavery issue in the case brought before it in behalf of Dred Scott, known as Dred Scott v. Sandford. In 1857, the decision by Chief Justice Roger B. Taney stated that Dred Scott, an enslaved person, remained enslaved despite having lived in free territories, and Black people could not be considered citizens of the United States. Moreover, it declared the Missouri Compromise unconstitutional, thus ruling that Congress could not prohibit slavery in any U.S. territories. This decision heavily contributed to the national division over slavery and ultimately to the Civil War.