What are the three things that heated up the slave debate and caused more tension between northern and southern states?

The heated debate over slavery was intensified by three main factors: the Missouri Compromise of 1820, which attempted to maintain a balance between free and slave states; the publication of "Uncle Tom's Cabin" in 1852, which exposed the brutal realities of slavery to a wider audience; and the Dred Scott decision in 1857, which ruled that African Americans could not be citizens and that Congress had no authority to regulate slavery in the territories. These events heightened sectional tensions and polarized opinions, ultimately contributing to the outbreak of the Civil War.