Missouri Compromise: An agreement reached in 1820 to maintain an equal balance between free states and slave states by admitting Missouri as a slave state and Maine as a free state.
Nullification Crisis: A dispute in the 1830s between the federal government and South Carolina over whether a state had the right to nullify or reject federal laws it deemed unconstitutional.
Election of 1860: The presidential election that ultimately led to Abraham Lincoln's victory and heightened sectional tensions, contributing to the secession of Southern states.