The Southern states seceded from the United Stated because they believed that the newly elected president, Abraham Lincoln, and his Republican majority were a major threat to the institution of slavery. Leaders in the South also wanted to preserve the rights of the states to govern themselves.
The debate over slavery had been raging since before the United States officially existed, but it had grown more bitter as the North pursued industrialism rather than agriculture, and the West attracted people who wanted to build small family farms, not giant plantations that needed slaves. Attempts to preserve a balance of power between slave states and free states, such as the Missouri Compromise of 1820 and the Compromise of 1850, helped paper over the sectional differences for a time. As the new states joined the union, however, the question of slavery kept arising.
The new Republican Party arose in the 1850s. Its platform opposed the expansion of slavery. When Abraham Lincoln, a Republican, won the election of 1860 with commanding majorities in both houses of Congress, Southern states panicked, worried that the federal government would not only stop the expansion of slavery, starving them of new markets for slaves, but also abolish slavery in the South, which they saw as an assault on their states' rights. These fears caused South Carolina, Mississippi, Florida, Alabama, Georgia, Louisiana, Texas, Virginia, Arkansas, Tennessee and North Carolina to secede and form the Confederate States of America.