Tobacco was initially the primary crop in the South, but soil depletion and price fluctuations led farmers to diversify into other crops like wheat, rice and sugar. However, limitations and failures of these crops resulted in cotton becoming dominant due to its hardiness, versatility and the development of the cotton gin which made processing easier. Cotton production spread throughout the South and by the Civil War it accounted for two-thirds of total US exports and $200 million per year in revenue. The rise of King Cotton drove a dramatic increase in the slave population as slavery expanded westward with cotton production. However, Southern manufacturing remained underdeveloped as the region remained economically dependent on cotton exports and invested in land and slaves rather than industry.