Final answer:
Short-staple cotton was king in the Southern economy because the cotton gin made its mass production possible, and it could be grown throughout the South.
Step-by-step explanation:
In the Southern economy, short-staple cotton was king. The invention of the cotton gin by Eli Whitney in 1793 made it economically viable to produce this type of cotton, which was well-suited for growth across the vast inland areas of the South. Unlike the long-staple cotton, which could only be grown along the coast and had long fibers and seeds that were relatively easy to remove, the short-staple cotton had shorter fibers and seeds that were difficult to remove, making the cotton gin an essential tool for its production. The gin significantly sped up the process of seed removal, allowing for mass production and making short-staple cotton a dominant force in the market. Together with slave labor, which was integral to the plantation system, these factors made cotton the foundation of the Southern economy.