The document discusses several key events in the buildup of tensions between free and slave states in the United States from the 1820s to 1860. It summarizes that the Missouri Compromise of 1820 aimed to balance slave and free states. It also discusses how the annexation of Texas as a slave state and the Mexican-American War increased tensions. The Kansas-Nebraska Act allowed settlers to vote on whether the territories would be slave or free, sparking violence. The Dred Scott decision upheld that slaves were property under the Constitution. John Brown's raid in 1859 further inflamed tensions, and Abraham Lincoln's election in 1860 without any Southern votes contributed to states beginning to secede.