What was a key factor in the election of 1860?

The election of 1860 was critically influenced by the significant division over the issue of slavery, making this the correct answer. At this time, the nation was experiencing deep sectional divides, particularly between the Northern and Southern states. The Democratic Party was split into Northern and Southern factions, largely reflecting varying views on slavery, which complicated the political landscape.

Additionally, the emergence of the Republican Party, which had a platform opposing the expansion of slavery into the territories, significantly altered the political dynamics. With Abraham Lincoln's nomination as their candidate, the Republicans consolidated anti-slavery sentiment in the North, which garnered considerable support. This division over slavery was not only a pivotal issue in the election but also foreshadowed the profound national conflict that would erupt into the Civil War shortly after.

In contrast, the other options do not adequately capture the complexity of the political situation at that time. The lack of unity among political parties, the public's engagement with slavery, and the presence of multiple candidates reflected a fragmented electorate rather than a cohesive political front. Understanding these divisions helps explain how the election of 1860 would lead to significant and enduring consequences for the United States.