Final answer:
The Supreme Court's decision in the Dred Scott case maintained that Dred Scott was enslaved, ruled Black people could not be U.S. citizens, and declared the Missouri Compromise unconstitutional, thereby also challenging the doctrine of popular sovereignty.
Step-by-step explanation:
In ruling on the Dred Scott case, the United States Supreme Court made several key determinations that had profound implications on the status of slavery in America. The court ruled that Dred Scott remained enslaved, declaring that Black people, whether free or enslaved, could not be considered citizens of the United States. This meant that they had no right to sue in federal court.
Furthermore, the Court declared the Missouri Compromise unconstitutional, stating that Congress had no authority to prohibit slavery in the territories. This effectively meant that the doctrine of popular sovereignty, which allowed territories to decide on the legality of slavery, was also challenged because it operated under the premise that Congress could indeed legislate on the issue of slavery in the territories.