How did the cotton gin make upland farming profitable

Farmers were able to plant more cotton.  Cotton is easy to grow but because it was so difficult to clean, cotton was not a cash crop.  Tobacco and indigo were the South’s cash crops.  Tobacco is difficult to grow.  Tobacco wears out the land and the land must be given a rest once every 7 years.  But cotton can grow anywhere, even on land that is drained of its nutrients. 
Now that cotton is easier to clean and since it grows easily, cotton became the number one cash crop in the South.  The farmers needed more land to grow cotton.  They took the land from the Native Americans.  The farmers needed more workers.  Slaves were the free labor that the farmers needed to harvest the cotton.