The document summarizes key events between 1820-1860 that heightened tensions between the North and South over the issue of slavery and led to Southern states beginning to secede from the Union. Some of the major events included the Missouri Compromise of 1820 allowing Missouri to enter as a slave state while banning slavery north of 36°30', the Mexican-American War and annexation of Texas expanding slavery, the Compromise of 1850 admitting California as a free state while strengthening the Fugitive Slave Act, the Kansas-Nebraska Act of 1854 establishing popular sovereignty, and the Dred Scott decision of 1857 declaring that Congress could not regulate slavery in the territories. John Brown's raid on Harper's Ferry in 1859