How was the Atlantic slave trade different in the 1400s from the 1600's?

In the 1400's there was no Atlantic slave trade. It didn't begin until the American colonies used the slaves as part of the triangular trade. The first slave arrived in 1619, but it wasn't until the invention of the cotton gin that the slave population grew to millions of slaves in the southern states. There is a direct relationship between the bales of cotton produced and the number of slaves.