As the United States expanded westward so did the issue of slavery. Southerners, forbidden to enter the Union with slaves, felt politically disadvantaged. In 1854 the Republican party was born in order to combat the Kansas-Nebraska Act, which proposed to extend slavery into the territories. Its aims were also to promote a modernization of the American economy, its natural supporters being business, large and small, and free, usually white, American labour, including free slaves. The Democratic party had split into the Southern Democrats, under John C. Breckinridge, and the Northern Democrats, led by Stephen Douglas, while a fourth party, the Constitutional Unionists, was led by John Bell. Much to the surprise of many Republicans, Abraham Lincoln emerged as the party’s leader. With Lincoln’s election what little remained of southerners’ sense of security was shattered. South Carolina was the first state to secede on 20 December 1860.