Answer:
After the American Revolution, and the establishment of a free United States from the colonies that had once been British property, agreement and peace did not ensue between them. There were several areas in which both the North and South states disagreed, and which eventually led to further conflict and to the endangerement of the entire nation. However, two of them stand out as the most important. The first, was, undoubtedly slavery, as it pertained to the territories that were annexed into the Union after the independence was reached, and the second, the level of involvement the federal government should have in regulating such matters as the economy and trade both between the states and with the outside world.
In the first case, slavery, the North and South differed in one essential point: the North wanted slavery to be abolished, while the South did not. The rift between the two regions was so great, and so insurmountable, that it became one of the reasons why the Civil War broke out. The real fight came because of the difference in views as to what was to be done with the territories that were starting to join the Union, whether slavery should be allowed to extend to these territories, or not. This would ensure whether the North, or the South, had the most power and control in the Union.
The second reason was the difference in views as to the level of involvement that the federal government should have in regards to regulation of commerce, state power, and especially the economy. As such, their views differed greatly on whether a Central Bank of the United States should be created, or not, whether protectionary tariffs should be set in place by the federal government, or if it was to be handled by the states, and finally, whether the federal government should be given the power to control internal improvements and thus use the nation´s taxes for such a centralized task, or if this should be given to each state independently.
The end result of these two factors, and others, led to the disastrous Civil War.