I believe black slavery began in the 1500s. English Captain John Hawkins would take ships to Africa, buy captured blacks from the local chiefs, (those not bought were eaten by the local blacks).
Hawkins then took his ships to South America where he sold slaves around the Caribbean until his fleet was captured and sunk by the Spanish at Vera Cruz.
Hawkins escaped to later fight against the Armada. His slaves, captured by the Spanish, were sold to profit Spain.
The Portuguese were the first to traffic in Black Slaves from Africa to the New World. Pope Paul III had issued a Papal Bull in 1537 prohibiting enslavement of the indigenous people of the New World, afterward the slave trade grew quickly.