What issue separated the north and south in 1861?

The primary issue that separated the North and South in 1861 was slavery. The Southern states relied on an economy based on agricultural production, which depended heavily on enslaved labor, while the Northern states were increasingly industrialized and opposed the expansion of slavery into new territories. This fundamental disagreement led to heightened tensions over states' rights, economic interests, and moral concerns, ultimately culminating in the secession of Southern states and the outbreak of the Civil War.