What was the circular trade that the Portuguese developed in their colonies?

The Circular trade that the Portuguese developed in their colonies was the trading of goods developed from metals for slaves from Africa.

Explanation:

The Portuguese were part of the colonial masters. They formed colonies and traded slaves based on the inspiration they got from seeing countries in Europe doing the same thing.

The Circular trade the Portuguese developed was a trade by barter system. They travel to countries in Africa and trade goods manufactured or produced from metal for African slaves. These slaves are then transported to America via ships from Brazil. The slaves are then put to work on Agricultural plantations as well as mines.