The most fundamental disagreement between the northern and southern states was over the issue of slavery. The southern states were largely agricultural, and their economies were heavily dependent on slave labor. The northern states, on the other hand, were more industrialized, and they did not have the same need for slaves. As a result, the northern states began to pass laws that restricted or abolished slavery. The southern states saw these laws as a threat to their way of life, and they began to resist them.