When did slavery start in America?
Slavery in America started in 1619. People (People referring to the Spanish) needed people to work on their plantations. Racism was already quite common. They would enslave the Native Americans and make them work on their land. This is were the idea that "People of darker skin are inferior to us" came from.
When Native Americans rebelled, ran off, and died due to disease the Spanish turned to Africa. They were relatively immune to the diseases, had no friends or family to help them escape, and could easily be told apart from the Spanish.