From Wikipedia

Congo

Part Two

By the 15th century CE, the farming Bakongo people (ba being the plural prefix) were unified as the Kingdom of Kongo under a ruler called the manikongo, residing in the fertile Pool Malebo area on the lower Congo River. The capital was M'banza-Kongo. With superior organization, they were able to conquer their neighbors and extract tribute. They were experts in metalwork, pottery, and weaving raffia cloth. They stimulated interregional trade via a tribute system controlled by the manikongo. Later, maize (corn) and cassava (manioc) would be introduced to the region via trade with the Portuguese at their ports at Luanda and Benguela. The maize and cassava would result in population growth in the region and other parts of Africa, replacing millet as a main staple.