The key issue leading to the American Civil War was slavery and its expansion into new territories. Tensions between the Northern states, where abolitionist sentiment was growing, and the Southern states, which depended on slave labor for their economy, escalated in the decades leading to the war. The Missouri Compromise, the Compromise of 1850, and the Kansas-Nebraska Act attempted to address the balance between free and slave states but ultimately failed. The election of Abraham Lincoln in 1860 alarmed Southern states, leading to the secession of several states and the formation of the Confederacy. These conflicts over slavery fundamentally shaped the causes and consequences of the Civil War.