There were a myriad of differences between the Northern and Southern regions, but I still don't understand how or why they grew similarities and united over time.
Does it have something to do with Enlightenment/Great Awakening? I know that both the North and South were hugely affected by it, but in what ways did they unite as a whole?
Sorry if it's a broad question, but please help me out the best way you can.
There were and are a myriad of cultural differences between the North and South of the USA. And between New England, the Midwest and the Pacific North West - all part of "the North". And between, California, the South East, Texas, the "deep" South and the South East - all part of the "South". And, of course, Alaska and Hawaii are each different in their own ways from the alleged monoculture of the continental United States.
However, if the question is about how and why these different cultures chose to become and remain part of the United States then the genesis lies in the fact that the 13 colonies that became the original states were all British colonies and they had that common bond between them. In addition, there was a fair dose of pragmatism: at the signing of the Declaration of Independence, when the colonies were already in rebellion, Benjamin Franklin reportedly said "We must all hang together, or assuredly we shall all hang separately."
Alternatively, if the question is about when the citizens of the United States began to think of the country more as an individual entity (which it is) rather than a federation of sovereign states (which it also is), some research has been done on the use of the phrase "the United States is" versus "the United States are" in decisions of the Supreme Court (admittedly the sample size is small). The latter phrase was overwhelmingly the most common at the beginning of the 19th century, dropping to about 50/50 by the start of the Civil War in 1861. Following the war, which was triggered by disputation between state and federal rights, the use of "are" increased to about 70% in the 1870s, 1880s and 1890s before vanishing completely by the 20th century. Taking this as a guide, the United States really was united around 1900.
The regions' cultures did not begin to unify before the Revolutionary War. They remained very different until the time of the Civil War, which is why the latter took place. What is true is that different regions of the 13 Colonies had common concerns, which united them sufficiently to make common cause against the British.
These common concerns included the following:
"No taxation without representation." The colonies all had local governments, and for the better part of 100 years, had submitted to taxation only by location legislatures. They were unwilling to submitted to taxes promulgated by "London," unless, perhaps, their local representatives were seated in Parliament (not likely, given the communications of the times).
The Quebec Act, which restricted settlement west of the Alleghenies to members of the 13 colonies, in favor of protecting Native Americans and Canadians.
"Mercantilism," whereby the colonists could not manufacture goods, but had to buy them from England.
Canadian locales for trials of political offenses; colonial juries were granting too many acquittals.
Quartering of troops in people's houses, without compensation.
The differences included the following:
High versus low tariffs for imported manufactured goods (the North wanted high, the South wanted low).
Large versus small landholdings; slave versus free labor. The South wanted large cash crop estates worked by slaves; the north favored small "freeholders."
Social diversity (or lack thereof). It may not be an accident that the term "ethnic purity" was coined by a southerner (Jimmy Carter) in the twentieth century. The South had two basic groups; white "Anglos" and black slaves. The North was much more diverse, at least with regard to European immigrants.
A few large (populationwise) vs. many small states. This lead to the establishment of two houses of Congress: the House of Representatives for large states, and the Senate, which favored small (often Southern) states.
