Final answer:
The labor on Spanish haciendas and plantations in the Americas was provided by unpaid Native Americans and enslaved Africans, under the encomienda system and through the Atlantic slave trade.
Step-by-step explanation:
The labor on Spanish haciendas and plantations in the Americas was primarily provided by unpaid Native Americans and enslaved Africans. Native laborers were often forced to work under the encomienda system, which granted Spanish encomenderos control over Native workers, with the pretense of offering protection and religious education. However, this system was essentially a form of slavery. As Native populations dwindled due to disease and harsh conditions, Africans were increasingly brought over through the Atlantic slave trade to work on plantations, enduring brutal treatment and resistance met with violence.