Final answer:
The primary motive for using enslaved labor in the cotton and sugar plantations in the Americas was the need for a controllable and cheap workforce for the Southern economy. Africans were seen as more profitable than indentured servants and Native Americans due to their physical resilience, cultural differences, and the religious argument for missionary work.
Step-by-step explanation:
The primary motive for using enslaved labor in the cotton and sugar plantations in the Americas, particularly African slaves, was the need for a large, controllable workforce that could produce crops like rice, cotton, and tobacco. Slavery provided a virtually limitless and cheap source of labor that was essential for the Southern economy. Unlike indentured servants and Native Americans, Africans were seen as a more profitable choice due to their physical resilience, perceived cultural differences, and the religious argument that they could be exposed to Christianity through missionary work.