Final answer:
The resistance and resilience of indigenous populations against forced labor.
Step-by-step explanation:
The major factor in Europeans starting to rely on Africans rather than indigenous Americans for labor on plantations was A. The resistance and resilience of indigenous populations against forced labor. Europeans found it difficult to control and exploit the indigenous populations due to their knowledge of the terrain and their resistance to forced labor. Africans were seen as a better labor force as they were less familiar with the land and were believed to be more susceptible to European diseases.