- The Kansas-Nebraska Act of 1854 repealed the Missouri Compromise and allowed settlers in those territories to decide whether to allow slavery, igniting tensions between North and South. - Abraham Lincoln was elected President in 1860 as the first Republican candidate, with no support from Southern states. In response, several Southern states seceded and formed the Confederate States of America. - The CSA was established with Jefferson Davis as President and a constitution that protected slavery. However, rising sectional tensions over the expansion of slavery led to the outbreak of the Civil War between the Union and the Confederacy in 1861.