What was the cause of South Carolina's desire to secede from the Union?

South Carolina's desire to secede from the Union was primarily caused by the issue of states' rights and the expansion of slavery. The election of Abraham Lincoln in 1860 was a critical event leading up to secession. Lincoln was a member of the Republican Party, which opposed the expansion of slavery into the western territories of the United States. South Carolinians and other Southerners feared that Lincoln's presidency would threaten the institution of slavery, which was fundamental to their economy and social structure.

Moreover, South Carolinians felt that their rights as a state were being infringed upon by the federal government. They believed in the doctrine of nullification, which held that a state had the right to nullify, or invalidate, any federal law that they deemed unconstitutional. They also believed strongly in the concept of "states' rights," or the idea that the powers of the federal government should be strictly limited and that all rights not explicitly granted to the federal government by the Constitution were reserved for the states.

The final straw came when Lincoln, whom South Carolinians saw as hostile to slavery, won the presidency. Shortly after his election, on December 20, 1860, South Carolina became the first state to secede from the Union, prompting other Southern states to follow suit and ultimately leading to the outbreak of the American Civil War.

The United States in the 19th century was deeply divided over the issue of slavery. The Northern states generally opposed the expansion of slavery into new territories and states, while the Southern states sought to protect and expand the institution. This division was rooted in economic differences; the Southern states' economies were largely dependent on agriculture and slave labor, while the Northern states were more industrialized and less reliant on slavery, though they too benefited economically from the institution.

The concept of states' rights was at the heart of South Carolina's argument for secession. The idea derived from a strict interpretation of the 10th Amendment to the U.S. Constitution, which states that the powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.

Tensions were exacerbated by several legislative acts and events, such as the passing of the Fugitive Slave Act as part of the Compromise of 1850, the Dred Scott decision in 1857 in which the Supreme Court ruled that Congress had no authority to prohibit slavery in the territories, and the Kansas-Nebraska Act of 1854 which allowed residents of territories to decide the legality of slavery for themselves through popular sovereignty.

South Carolina's secession led to the formation of the Confederate States of America, consisting of eleven Southern states that seceded from the Union. The conflict between the North (the Union) and the South (the Confederacy) erupted into the Civil War in April 1861, which lasted until 1865 and resulted in the end of slavery and the preservation of the Union. The Civil War remains one of the most devastating conflicts in American history, with profound effects on the nation's subsequent development.