Final answer:
The Democratic Party nominated two presidential candidates in the 1860 election, Stephen A. Douglas and John C. Breckinridge, due to an internal split over slavery, which aided Abraham Lincoln's victory and presaged the Civil War.
Step-by-step explanation:
The tumultuous atmosphere surrounding the presidential election of 1860 stems from the deep divide within the Democratic Party over the issue of slavery. This internal conflict came to a head during the party's nominating convention in Charleston, South Carolina. Here, the disagreement over a pro-slavery platform caused Southern delegates to walk out, leaving the party unable to secure a two-thirds majority for any single candidate. Consequently, the Democrats nominated two separate candidates: Stephen A. Douglas by Northern Democrats and John C. Breckinridge by Southern Democrats.
The fracture within the Democratic Party presented an advantage to the Republicans, who ran Abraham Lincoln as their sole presidential candidate. Lincoln's ensuing victory in the election indicated how the division among Democrats helped splinter the vote. This schism not only affected the election's outcome but also foreshadowed the coming secession of Southern states and the onset of the Civil War.