1. Slavery: slavery was the main issue that divided the United States in the 19th century. The Southern states were largely agricultural, and their economy depended on the labor of enslaved African Americans. The Northern states, on the other hand, were becoming industrialized and did not have the same need for slavery. The issue of slavery led to numerous debates, conflicts and tensions between the Northern and Southern states, eventually culminating in the Civil war.
2. States' Rights: The issue of states' rights also played a crucial role in the Civil War. The Southern states argued that they had the right to make their own laws and govern themselves as they saw fit, including the right to keep slavery. The Northern states believed that the federal government had supremacy over the states and could intervene in cases of injustice or violation of the Constitution. This disagreement over states' rights further deepened the divide between the North and the South and contributed to the outbreak of war.