What was the first Southern U.S. state to secede from the Union?

South Carolina was the first Southern state to secede from the Union, doing so on December 20, 1860, shortly after the election of Abraham Lincoln. State leaders feared that Lincoln's opposition to the expansion of slavery threatened their economic and political interests. South Carolina's decision triggered a wave of secessions across the South, ultimately leading to the formation of the Confederate States of America. Within months, ten additional Southern states had left the Union, setting the stage for the outbreak of the American Civil War.