The correct answer is inventing the cotton gin.
The cotton gin was a machine that easily removed seeds from cotton. This rapidly increased the ability of farmers and slaves to produce cotton. After this invention was implemented, slaves could clean over 200 pounds of cotton in a day. This was incredible, considering before this time (when the process was done by hand) a slave could only clean about 1 pound a day.
Even though this machine was supposed to make the lives of slaves easier, it had the opposite effect as slavery increased in the Southern states due to the ability to generate a large profit off this good.