What was the primary reason that the spanish and portuguese turned to enslaved africans as a source of labor for their mines and farms in the new world?

When Portugal and Spain established the first American colonies, they encountered difficulties turning the native American people into a slave labor force that is why they introduced Africans as a labor source in the New World force

To work as slave laborers, because after the Native Americans died from European disease and most of them escaped, the British turned to Africans to be the next source of production. Africans were more immune to their diseases, because they were used to the climate areas. You're welcome:)