For what primary purpose did the Spanish enslave many American Indians?

When Columbus discovered the New World, he was in need of more money to continue his explorations. He captured many slaves and sold them in Spain. Enslavement was viewed to be good for the country's economy. Labor was gotten for free. When more Spanish conquerors went to America, many American Indians were used to carry their shipments back and forth their territory and ships. The Spaniards justified their actions by saying that the Indians were cannibals and deserved to be punished through enslavement.