In the early years of American history after the revolution but before the Civil War, slavery was an enormous driver of wealth and profit. Though the practice of chattel slavery was only legal in the South, the manufacturing sector that existed in the North heavily relied on the free labor from slaves to buy raw materials at rock bottom prices. It is hard to overstate how integral the millions of hours of forced labor were to the creation of the American economy.
As far as structure goes, the move out of the 1700's into the 1800's brought the industrial revolution into focus. America shifted from a rural, agrarian nation that mainly relied on extraction of natural resources to create wealth to an industrial nation that was driven by manufacturing in the cities. The American economy would be dominated by manufacturing jobs until the middle of the 20th century, which brought about a slow but definite decline. While there will always be farming jobs and manufacturing jobs somewhere in the country, we are now characterized by our dearth of service industry jobs.