Slavery and the Sectional Crisis

Eli Whitney's cotton gin (1793) transformed the profitability of cotton and drove the expansion of slavery across the Deep South; by 1860 the enslaved population of the United States had reached roughly 3.9 million, and Southern cotton accounted for more than half the total value of American exports. The North, meanwhile, developed an increasingly industrial, urban economy built on free wage labor, and gradual abolition in Northern states — beginning with Pennsylvania in 1780 — hardened a growing division between "free states" and "slave states," a divide already embedded in the Constitution's three-fifths clause and its protection of the slave trade until 1808.