Which state was first to secede and on what grounds?

South Carolina was the first state to secede from the Union on December 20, 1860. The primary grounds for its secession were concerns over states' rights and the perceived threat to the institution of slavery, particularly in light of the election of Abraham Lincoln, who was seen as hostile to the interests of slaveholding states. South Carolina's leaders believed that secession was a necessary step to protect their way of life and maintain their sovereignty.