Why did Spanish colonists begin to rely more heavily on the Atlantic slave trade by the mid-1500s?
A. Spain had established new African colonies and had begun to
enslave their populations.
B. Fewer Spanish servants were willing to travel to and work in the
colonies.
C. Legal restrictions and outbreaks of disease made it difficult to get
sufficient labor from indigenous populations.
D. Indigenous populations gained independence and liberated
themselves from forced labor.

help please asap!