The Whig Party, which was an anti-Jackson alliance between Southern Republicans and Northern Democrats, disintegrated in the 1850s over the increasingly contentious issue of slavery. In its place, the Republican Party arose as the chief political opposition to the Democrats. The Republican Party crystallized in opposition to slavery, while the Democrats supported the institution.

The Kansas-Nebraska Act divided the Whigs Southern pro-slavery and Northern antislavery components. The fractures ran so deep that even Northern Whigs were divided, between antislavery “Conscience Whigs” and conservatives who supported the Compromise of 1850. This split forced many antislavery Whigs to look for a political alternative less muddied by internal conflict.

One alternative was the American Party, which became known as the Know-Nothing Party because the members met secretly and refused to identify themselves. This party was a nativist organization (anti-foreigner) that spread anti-German, anti-Irish, and anti-Catholic propaganda. Most members also favored temperance and opposed slavery. It seemed the Know-Nothings would form the primary opposition party to the Democrats until, in 1855, they also succumbed to sectional conflict when the party’s Southern branch made acceptance of the Kansas-Nebraska Act part of the Know-Nothing platform. The Know-Nothing party found itself weakened and near ruin.

In its place, a new Republican Party emerged as the premier antislavery coalition. The Republicans originally formed in the North between 1854 and 1855, as Northern Democrats, antislavery Whigs, and former Free Soil party members united to oppose the Democratic Party. Although all Republicans disapproved of the Kansas-Nebraska Act, some Republicans merely wanted to restore the Missouri Compromise. Others were middleground free-soilers, and still others were adamant abolitionists. Nevertheless, opposition to slavery’s extension united these disparate groups.

In the 1858 midterm elections, Republicans and Democrats faced off for the first time. The most visible of these battles took place in Illinois, where prominent Democratic Senator Stephen A. Douglas faced a reelection challenge in the form of Republican Abraham Lincoln. This campaign pitted the Republican Party’s rising star, Lincoln, against the Democratic Party’s leading senator. In a series of seven debates known as the Lincoln-Douglas Debates, Douglas advocated popular sovereignty while Lincoln espoused the free-soil argument.

Douglas painted a picture of his opponent as an abolitionist and an advocate of racial equality and racial mixing, positions that were still very unpopular at the time. Lincoln countered that he was not an abolitionist—that he simply opposed the extension of slavery into the territories, but did not aim to abolish slavery where it already existed, in the South. He further claimed, “I have no purpose to introduce political and social equality between the white and the black races ,” but still argued that “notwithstanding all this, there is no reason in the world why the negro is not entitled to all the natural rights enumerated in the Declaration of Independence.” In attack of his opponent, Lincoln challenged that Douglas’s belief in popular sovereignty, in particular his “Freeport Doctrine,” was incompatible with the Dred Scott decision. In this doctrine, Douglas stated that territorial governments could effectively forbid slavery by refusing to enact slave codes, even though the Dred Scott decision had explicitly deprived Congress of the authority to restrict slavery in the territories.

In the end, neither candidate emerged from the debates as the clear victor. Although Douglas won the Senate seat, he alienated Southern supporters by encouraging disobedience of the Dred Scott decision with his Freeport Doctrine. Lincoln, meanwhile, lost the election, but emerged with national prominence as a spokesman for antislavery interests.

In 1860, Buchanan announced he would not run for reelection. The Democratic Party ruptured over whom to nominate in Buchanan’s place. While Northern Democrats defended the doctrine of popular sovereignty and nominated Stephen Douglas for president, Southern Democrats opposed popular sovereignty in favor of the Dred Scott decision—which provided absolute protection of slavery in all territories—and nominated vice president John Breckenridge for president. Southern moderates from the lower South walked out of the Democratic Convention and formed their own party, the Constitutional Party, which nominated John C. Bell for president. These three candidates faced Republican nominee Abraham Lincoln.

Lincoln emerged with a majority of the electoral votes, 180 in total. He carried all eighteen free states, but had not even appeared on the ballots of a number of slave states, and in 10 slave states, had not received a single popular vote. Lincoln’s election so alienated the South that secession seemed imminent. While South Carolina had threatened earlier to secede from the Union over the Tariff of Abominations in 1828, the current threat was much more dire.