There was a clear difference between the states in the north and the others farther south already from the start even though all of them had settled along the Atlantic shores.
The natural conditions, that is the climate and the soil, were favorable for plantation farming in the South. In the beginning the farming there was kept on a small scale. The soil was worked by the owners themselves and a few contract workers from Europe.
By the end of the 17th century, Negro slaves were imported from Africa and did most of the work. As the plantations were growing bigger in the 18th century, some of them had several hundred slaves.
Towards the end of the 18th century, cotton became the main crop in the area between South Carolina and Texas.
The most important reason for the plantation owners to the plant cotton in the South were the favorable economical conditions. The slave based economy gave very good profits to the owners.
In the North, the natural conditions invited to small farming only. The people there were small farmers, fishermen, craftsmen and merchants.
They also lived mostly in small villages, and each village was one congregation. The point is that the people who settled in the northern colonies were religious people who went to America to found a new Christian society without social differences.
These facts led to the development of a different social structure in the North with more equality both economically and socially. In the South, where they kept slaves to do the work on the plantations, the society was built on inequality and the suffering of the black population.
The reason for the war
The northern states were very much against the system of slavery. This disagreement lead in the end to the war between the North and the South. Since the war was fought between people belonging to the same nation, it was called the Civil War.