a. South Carolina: because it thought the federal government violated its obligation in states
South Carolina seceded from the Union in December 1860 and was the first southern state to leave.
South Carolina believed they had the right to secede because they ratified the Constitution and it was a contract. They essentially took back their ratification in their secession message to Congress. Many of the southern colonies including South Carolina stated a violation of their rights as states for the reason to leave the Union. Much of this decision was tied to the victory of Lincoln in the 1860 election.