Final answer:
African slaves were used as the primary labor source for cotton and sugar plantations in the Americas because they were seen as more physically resilient and less likely to escape than Native Americans, and they could be enslaved for a lifetime whereas Europeans succumbed to diseases and legal protections limited the use of indentured servants.
Step-by-step explanation:
The reason African slaves were used primarily for forced labor in the cotton and sugar plantations in the Americas, instead of indentured servants or Native Americans, was multifaceted. European settlers preferred workers unfamiliar with the land, which made Africans less likely to escape successfully compared to Indigenous people. Furthermore, many Europeans perished quickly due to the hot Caribbean climate and diseases like malaria and yellow fever, which deterred further immigration for indentured servitude. In contrast, Africans, who were also not dying from European diseases at the same rate as Native Americans, were seen as more physically resilient and could be enslaved for life, providing a constant labor source. Additionally, the average indentured servant, often migrating voluntarily, could not satisfy the vast labor demands of plantations, and legal restrictions on the treatment of indentured servants made them less desirable to European colonists.