Final answer:
The 1857 Supreme Court decision in the Dred Scott case repealed the Missouri Compromise by ruling that Black people could not be U.S. citizens and that Congress could not prohibit slavery in federal territories.
Step-by-step explanation:
The Supreme Court's decision in the Dred Scott case in 1857 effectively repealed the Missouri Compromise. The historical case of Dred Scott v. Sandford, decided by the Supreme Court, ruled that Black people, whether free or enslaved, could not be citizens of the United States, and therefore, Dred Scott, an enslaved African American who had lived in free territories, had no legal standing to sue for his freedom. Additionally, the court declared that Congress lacked the power to prohibit slavery in the territories, making the federal government unable to pass laws limiting the expansion of slavery into any part of the West.