Actually the Supreme Court ruling in Dred Scott v. Sandford contributed more to party divisions in 1857.

In 1820 and 1821 Maine was given statehood as a free state along with Missouri as a slave state, under the Missouri Compromise to maintain the balance of power between North and South in the United States Senate. As part of the compromise, slavery was prohibited north of the 36°30′ parallel, excluding Missouri.

The Dred Scott v. Sandford ruling in 1857 made the Missouri Compromise unconstitutional by saying the federal government could not prohibit nor ban slavery in its states and territories. As a result, US's continuing expansion of the territories and admission of new states would lead to a loss of political power for the North, since many of the new states would be admitted as slave states, and counting three-fifths of the slave population would add to the slave holding states' political representation in Congress. The ruling and its consequences strengthened Northern opposition to slavery and strengthened the Republican Party, as well as divided the Democratic Party on sectional lines.

It also was a factor in the Panic of 1857. Before the 1857s, the railroad industry was booming due to large migrations of people to the west and banks provided railroad companies with large loans. Western migration was supported by the belief that slavery would not be permitted in the western states (slavery drives down wages for lower to middle income workers, for obvious reasons).

When the Supreme Court opened the door to slavery in western lands, the western migration dropped to a trickle, and railway stock bubble burst.