<P> When the new Republican Party formed in 1854 on the basis of refusing to tolerate the expansion of slavery into the territories, many northern Democrats (especially Free Soilers from 1848) joined it . The Republicans in 1854 now had a majority in most, but not all of the Northern states and it had practically no support South of the Mason--Dixon line . The formation of the new short - lived Know - Nothing Party allowed the Democrats to win the presidential election of 1856 . Buchanan, a Northern "Doughface" (his base of support was in the pro-slavery South), split the party on the issue of slavery in Kansas when he attempted to pass a federal slave code as demanded by the South . Most Democrats in the North rallied to Senator Douglas, who preached "Popular Sovereignty" and believed that a Federal slave code would be undemocratic . </P> <P> The Democratic Party was unable to compete with the Republican Party, which controlled nearly all northern states by 1860, bringing a solid majority in the Electoral College . The Republicans claimed that the Northern Democrats, including Doughfaces such as Pierce and Buchanan, as well as advocates of popular sovereignty such as Stephen A. Douglas and Lewis Cass, were all accomplices to Slave Power . The Republicans argued that slaveholders (all of them Democrats) had seized control of the federal government and were blocking the progress of liberty . </P> <P> In 1860, the Democrats were unable to stop the election of Republican Abraham Lincoln, even as they feared his election would lead to civil war . The Democrats split over the choice of a successor to President Buchanan along Northern and Southern lines: factions of the party provided two separate candidacies for President in the election of 1860, in which the Republican Party gained ascendancy . </P> <P> Some Southern Democratic delegates followed the lead of the Fire - Eaters by walking out of the Democratic National Convention at Charleston's Institute Hall in April 1860 and were later joined by those who, once again led by the Fire - Eaters, left the Baltimore Convention the following June when the convention rejected a resolution supporting extending slavery into territories whose voters did not want it . The Southern Democrats nominated the pro-slavery incumbent Vice President, John C. Breckinridge of Kentucky, for President and General Joseph Lane, former governor of Oregon, for Vice President . </P>

What issue split the democratic party in 1860