Where were African slaves first brought to work?

The first African slaves used by Europeans were used by the Portuguese, on the island of Sao Tome, to grow sugarcane. The Spanish were the first to use African slaves in the Americas (in the Caribbean), and the first English colony to use African slaves was Jamestown, Virginia (which was the first English colony in the New World).

However, long before Europeans used African slaves, the Africans had slaves who were African!