What impact did the growing demand for labor in the Americas have on justifications for slavery ?

When the Civil War began in 1861, the South was rich. It had a successful economy with a very high number of millionaires per capita. Its economy was dependent on slavery. How did that happen?
From the onset of colonial settlement in the early seventeenth century, laborers were needed. At first, most of these laborers were indentured servants; indentured servants worked a number of years to pay for their passage to America before becoming free. By the late seventeenth century, however, it was clear that indentured servitude would not continue to provide enough workers. More jobs had become available in England, so too few people were willing to come to America as indentured servants.
From then on, slaves were increasingly seen as an essential labor force, particularly in the agricultural South. Moreover, the invention of the cotton gin in 1793 made slavery an institution. The cotton gin and a large slave labor force made the South the primary producer of cotton. Although the slave trade was ended in 1807, the cotton industry flourished and expanded during the first third of the nineteenth century. In the urban North, slavery was never essential, and the institution died out.
By the mid-nineteenth century, the North and South were constantly arguing about slavery. Finally, the Civil War (1861–1865) settled the question.