What contributed to the rise of the kingdom of Kongo?

The rise of the Kingdom of Kongo was that many people got attracted to Kongo because of the rich gold mines at Sofala. Also, they have been pushing intermarriage with the African people to gain favor and pushing farther into the interior of Africa. Aside from that people also developed skills like weaving, pottery, blacksmithing, and carving which have also contributed to their economy. Also, the agriculture was a big part in Kongo.