The North and South diverged because of slavery in the South and increasing industrialization in the North.
Petroleum (oil) was first discovered in North Dakota in 1951 and greatly increased North Dakota's wealth.
There was a lot of immigration to the North, plus the growth, industry, and the population grew a lot in the decades before the Civil War.
Christianity, especially Protestant denominations
rapid expansion of industry
As a region, the South depended almost entirely on "King Cotton" in the long decades preceding the Civil War. To the exclusion of manufacturing, trade, and other industrial (and even agricultural) accomplishments in the North, Southern business and political leaders invested the majority of their time, money, and energy into cotton and cotton alone.
The south believed in inbreeding greatly among each other and the north did not.
No. "Of a city" needs to modify a preceding noun, and "northern" is an adjective, rather than being a noun. But "northern part of a city" or "north of a city" would both be okay, because "part" and "north" can be nouns. I don't understand why "of a city" needs to modify a preceding noun, however (if that is really true). In some other examples, a prepositional phrase with "of" can go with a preceding adjective -- for instance in "desirous of being chosen".
the temperature goes up greatly
Greatly speeding the movement of troops and supplies.
the north American free trade agrrement
Spain had the most territory in North America in 1790. However, in the next few decades, it would be the UK and then the US.
Dean Smith, with North Carolina