The Industrial Revolution, as this era is called by historians, is generally traced back to Britain in the 1700's with the advent of the creation of interchangeable parts and assembly line production in a factory setting. Samuel Slater is credited with memorizing the plans to one such factory and bringing his ideas to the United States (where he became a successful factory owner/businessman known for employing children under the age of twelve, as was proving successful in England). The invention of the cotton gin by Eli Whitney in 1793 proved to be perfect timing for Slater and others in the factory business, as this equipment made it much faster to clean cotton and get it ready for its transformation into fabric. This invention also provided the South with a whole new way to utilize their slaves making exponentially more money; where one slave might need all day to pick a pound of cotton clean, now they were producing far more clean cotton in the same amount of time.
So as the North was becoming more industrialized with the cotton gin, for example, the South was actually using the same machine to dig its heels in even further into the agricultural lifestyle that was built around slavery and rapidly going out of style in the North. In other words, the North was moving forward, but the South stayed put, and the more slaves owned by a planter, the more money he was going to make with the new cotton gins.
As the nation approached Civil War, a number of things increased sectional tension, including the slavery issue, especially as the abolitionist movement gained momentum in the North, and problems in Congress as representatives from North and South clashed over legislation and policies that, because of the very different economies of North and South usually benefited one section, but not the other.