Final answer:
Sectionalism, driven primarily by disputes over slavery, was a crucial factor in the election of 1860, leading to the Democratic Party's split and the Republican Party's win with Abraham Lincoln. The election outcome precipitated the secession of Southern states, heralding the onset of the Civil War.
Step-by-step explanation:
Sectionalism profoundly impacted the election of 1860, underscoring the deep divisions within the United States over the institution of slavery. In the years leading up to the election, events such as the Dred Scott decision, the Lincoln-Douglas debates, and John Brown's raid on Harper's Ferry exacerbated these divisions, with the Democratic Party ultimately splitting into three factions over the slavery issue.
This schism within the Democratic Party, which had been one of the few remaining national institutions, gave the Republican Party - a party with a strong anti-slavery platform - a significant advantage. When the Republicans secured the presidency with Abraham Lincoln's election, it solidified the fears of the southern states, leading South Carolina and six other states to secede from the Union, setting the stage for the Civil War.
The Dred Scott decision declared that African Americans could not be citizens and that Congress had no power to regulate slavery in the territories, which inflamed Republican opposition and made their anti-slavery platform seem unconstitutional. Additional occurrences like 'Bleeding Kansas' further pushed the issue of slavery to the forefront of political discourse. Ultimately, the election's outcome fell along sectional lines, reflecting the stark divide between the North, which leaned Republican, and the South, which leaned Democrat and was pro-slavery.