By the 1850s America was growing around three fourths of cotton produced on the Earth, most of this cotton was shipped to England or New England where it would be turned into cloth. During this boom of the production of cotton, tobacco lost some of its value, rice pretty much stayed the same. However, like many inventors, Whitney could not have predicted the ways in which his invention intended for good made things a lot worst. The biggest impact that of these was the exponential growth of slavery.
While it was true that the cotton gin reduced the labor of removing seeds, it did not reduce the need for slaves to grow and pick the cotton. In fact, the opposite occurred. Cotton growing became so profitable for the planters that it greatly increased their demand for both land and slave labor.