Final answer:
Cotton was "King" in the Southern economy due to its immense profitability and the dependency on this crop by plantation owners, international markets, and the economic system that included enslaved labor as an essential component for its production.
Step-by-step explanation:
In the antebellum South, before the Civil War, cotton emerged as the paramount commercial crop and was indisputably "King" in the Southern economy.
The development of the cotton gin by Eli Whitney in 1793 led to a tremendous surge in cotton production, making it far more profitable than other crops like tobacco, rice, and sugar. By 1860, the South produced two-thirds of the world's supply, and the economy of the Southern United States was heavily reliant on this crop.
The cultivation of cotton was so interwoven with the institution of slavery that the two could hardly be separated; the demand for cotton fueled the demand for slave labor, which in turn bolstered the profitability of cotton plantations.
The importance of cotton to the Southern economy extended beyond agriculture into international markets, making it the primary cash crop and export, far surpassing the significance of other Southern crops and industries at the time.
Cotton's supremacy endured even into the Reconstruction era, as shown by the expansion of sharecropping and the continued reliance of the economy on this single crop.