The correct answer is B) the invention of the cotton gin.
The event that led to a rapid increase in the number of slaves in the South was the invention of the cotton gin.
Eli Whitney was the inventor of the cotton gin. This new machine was an immediate success in that it included a more efficient process to remove the seeds from the fiber of the cotton, accelerating the process of production of cotton. The invention was more than well-received by plantation owners that needed more slaves to operate the machines and produced more cash crops to trade and export.