Final answer:
The cotton gin, invented by Eli Whitney in 1793, helped cotton become the foundation of the South's economy by greatly enhancing the efficiency of cotton processing.
Step-by-step explanation:
The invention that helped cotton become the foundation of the South was the cotton gin, created by Eli Whitney in 1793. This revolutionary device efficiently removed seeds from the short staple cotton, which was more abundant but harder to process than the long staple variety. This allowed Southern planters to efficiently produce large quantities of cotton, making it the dominant crop in the region and a crucial element of the international market.
Although Whitney's invention was intended to reduce the need for slave labor, it had the opposite effect. The increased demand for cotton led to a greater reliance on the institution of slavery, with the South's economy becoming heavily dependent on both the crop and the forced labor used to produce it. The intertwining of cotton production and slavery ultimately became a defining characteristic of the antebellum South, setting the stage for the Civil War.