Why do the Spanish need a new labor source?

Soon after his famous 1492 voyage, with the backing of the Spanish Crown and over one thousand Spanish colonists, Genoese merchant Christopher Columbus established the first European colony in the Americas on the island of Hispaniola (present-day Haiti and the Dominican Republic). Columbus is believed to have had prior experience trading in West Africa, and had certainly visited the Canary Islands, where indigenous people known as Guanches had long been enslaved and exported, in small numbers, back to Spain.