Missouri Compromise: An agreement in 1820 that admitted Missouri as a slave state and Maine as a free state to maintain the balance between slave and free states in Congress.
Kansas-Nebraska Act: A law passed in 1854 that allowed popular sovereignty (allowing residents to vote) on the issue of slavery in Kansas and Nebraska territories, leading to violent clashes between pro-slavery and anti-slavery supporters.
Dred Scott Decision: A Supreme Court ruling in 1857 that determined enslaved individuals were property with no rights, which further fueled tensions over the expansion of slavery into new territories.