Question: what was one reason south carolina gave for its decision to secede from the union?
Answer: to preserve slavery

Alfred P. Aldrich, a South Carolinian politician from Barnwell, stated that declaring secession would be necessary if a Republican candidate were to win the 1860 U.S. presidential election, stating that it was the only way for the state to preserve slavery and diminish the influence of the anti-slavery Republican Party, which, were its goals of abolition realized, would result in the "destruction of the South":