Final answer:
The Encomienda system was used by the Spanish to convert American Indians to Christianity and exploit their labor, ultimately resembling a form of forced labor similar to chattel slavery.
Step-by-step explanation:
The system employed by the Spanish that advanced the goals of both converting American Indians to Christianity and exploiting their labor was the Encomienda system. This system involved assigning Native American workers to mine and plantation owners under the guise of providing protection and religious instruction. However, in practice, the Encomienda system amounted to forced labor and exploitation, wherein the encomenderos (recipients of encomiendas) exerted total control over the native workers, often under brutal conditions. The labor system was criticized by figures such as Bartolome de Las Casas, a priest who advocated for reform. Despite its purported intentions of cultural and religious education, the Encomienda system was starkly similar to chattel slavery and only later was it replaced by the slightly less oppressive repartimiento system.