Bantu Migration
Some historians think that Bantu peoples began settling in the extreme northwest of Central Africa in the beginning of the 5th century and then gradually started to expand southward.
Their propagation was accelerated by the transition from Stone Age to Iron Age techniques. The people living in the south and southwest were mostly San and hunter-gatherer groups, whose technology involved only minimal use of metal technologies. The development of metal tools during this time period revolutionized agriculture and animal husbandry. This led to the displacement of the hunter-gatherer groups in the east and southeast.
The 10th century marked the final expansion of the Bantu in West-Central Africa. Rising population soon made intricate local, regional and foreign commercial nets possible, forming networks that traded mostly in salt, iron and copper.
Read more about this topic: Early Congolese History