(1860–61) Withdrawal of 11 Southern states from the U.S. The precipitating event was the election of Abraham Lincoln as president (1860). Since the Republican Party strongly opposed slavery and its extension into the new territories, most slaveholding states had vowed to secede if the Republican candidate won. Secession had been proclaimed by states'-rights advocates as a corollary to the compact that united the states, permitting them to withdraw as easily as they had joined. Earlier threats of secession were made at the Hartford Convention (1814), in the nullification crisis (1832), and in the 1850s before the Missouri Compromise. Secession was first approved by South Carolina (1860); six other states followed in the period before Lincoln was inaugurated in March 1861. After Lincoln resisted the South's attack on Fort Sumter, four other slaveholding states voted to secede, joining the newly formed Confederate States of America.