<P> In the colonial era, small amounts high quality long - staple cotton was produced in the Sea Islands off the coast of South Carolina . Inland, only short - staple cotton could be grown but it was full of seeds and very hard to process into fiber . The invention of the cotton gin in the late 1790s for the first time made short - staple cotton usable . It was generally produced on plantations ranging from South Carolina westward, with the work done by black slaves . Simultaneously, the rapid growth of the industrial revolution in Britain, focused on textiles, created a major demand for the fiber . Cotton quickly exhausts the soil, so planters used their large profits to buy fresh land to the west, and purchase more slaves from the border states to operate their new plantations . After 1810, the emerging textile mills in New England also produced a heavy demand . By 1820, over 250,000 bales (of 500 pounds each) were exported to Europe, with a value of $22 million . By 1840, exports reached 1.5 million bales valued at $64 million, two thirds of all American exports . Cotton prices kept going up as the South remained the main supplier in the world . In 1860, the US shipped 3.5 million bales worth $192 million . The mixture of a Mexican strand with existing strands of cotton led cotton bolls to open wide like a flat hand at harvest, which dramatically raised the amount of cotton that could be picked per day . </P> <P> After the Civil War, cotton production expanded to small farms, operated by white and black tenant farmers and sharecroppers . The quantity exported held steady, at 3,000,000 bales, but prices on the world market fell . Although there was some work involved in planting the seeds, and cultivating or holding out the weeds, the critical labor input for cotton was in the picking . How much a cotton operation could produce depended on how many hands (men women and children) were available . Finally in the 1950s, new mechanical harvesters allowed a handful of workers to pick as much as 100 had done before . The result was a large - scale exodus of the white and black cotton farmers from the south . By the 1970s, most cotton was grown in large automated farms in the Southwest . </P>

What would account for the large increase in the population of the midwest after 1860