Answer: An issue over the institution of slavery.
Explanation: The North was generally anti-slavery and supported abolitionists such as Harriet Beecher Stowe and John Brown to end this practice as they felt it was morally wrong. Whereas the South wanted the free labor and felt as though slaves were property with anti abolitionists such as Robert E. Lee and Jefferson Davis. They came to many compromises to avoid war such as the Compromise of 1820 and 1850 however these weren’t enough and eventually led to the Civil War.