After the passage of the Kansas-Nebraska Act in 1854, violence erupted between pro-slavery and anti-slavery settlers in Kansas territory, known as Bleeding Kansas. This violence was one of the first signs of open conflict between North and South and helped catalyze the formation of the Republican Party in opposition to the expansion of slavery. Other events exacerbating sectional tensions included the Dred Scott decision, John Brown's raid on Harpers Ferry, and Abraham Lincoln's election in 1860 without any Southern states, leading several Southern states to secede and form the Confederate States of America. The Civil War began with the Confederate attack on Fort Sumter in April 1861. Major battles included Antietam, Gettysburg, V