Soldiers were the first Spaniards who came to New Spain. They knew a lot about fighting, of course. But they were not ready to work in mines or farm for food. For that kind of hard work, these early settlers used the American Indian population.
Spain had a system called the encomienda. Under it, the Spanish king gave the labor of some American Indian groups to certain settlers for life. This basically meant that many American Indians of New Spain were held in slavery. Slavery is the practice of forcing people to work against their will without pay. Many enslaved American Indians were overworked. They were not fed well. They got sick from new diseases that settlers didn’t know they had brought from Europe. Not surprisingly, many natives died. In New Spain’s first 100 years, the American Indian population shrank a lot. It went from about 25 million to 1 million.