By means of land-labor grants called spanish entrepreneurs were entitled to use forced indigenous or imported slave labor to exploit natural resources in the new world.

The answer to the question above is Encomienda.
By means of land-labor grants called encomienda, Spanish entrepreneurs were entitled to use forced indigenous or imported slave labor to exploit natural resources to the New World. Encomienda is a Spanish labor system in which a colonists has the right to demand tribute and forced labor from the local inhabitants of the colony.

the South so abolitionism as a major threat to the way of life especially because the North granted slaves their freedom in exchange for fighting in the side of the union