Final answer:
The Dred Scott decision of 1857 ruled that Congress could not prohibit slavery in the territories, widening the national divide over slavery and contributing to the split between North and South, which would culminate in the Civil War.
Step-by-step explanation:
The Dred Scott decision of 1857 had profound implications for the legality of slavery in the United States. The Supreme Court ruling in Dred Scott v. Sandford declared that African Americans could not be considered citizens and could not sue in federal court. Furthermore, the Court stated that Congress had no authority to prohibit slavery in U.S. territories. This effectively made slavery legal in all territories, nullifying the Missouri Compromise, and threatened to expand slavery westward.
This decision compounded the already burgeoning divide within the nation regarding the issue of slavery. It infuriated the Republican Party, rendering their goal to prevent the spread of slavery unconstitutional. The ruling also posed a problem for northern Democrats like Stephen Douglas, who had proposed the notion of popular sovereignty as a compromise. The northern perspective saw this as evidence of the South's 'Slave Power' extending its influence to the Supreme Court. Conversely, southerners viewed the decision as a protection against northern abolitionist movements, securing the institution of slavery.
The sectional divide grew as a result, with figures like Abraham Lincoln articulating the Republican opposition in the debates with Stephen Douglas, and events such as John Brown's raid on Harper's Ferry heightening tensions. The Dred Scott decision was seen by many in the North as a direct challenge to their values and societal vision, escalating the conflict that would eventually lead to the Civil War.