A wave of early people was identified in the northern and north-western parts of central Africa during the second millennium BC. They produced food (pearl millet), maintained domestic livestock and developed a kind of arboriculture mainly based on the oil palm. From 1,550 BC to 50 BC, starting from a nucleus area in south Cameroon on both banks of the Sanaga River, the first Neolithic peopling of northern and western central Africa can be followed south-eastwards and southwards.
In D.R. Congo, the first villages in the vicinity of Mbandaka and the Lake Tumba are known as the Imbonga Traditions, from around 650 BC. In Lower Congo, north of the Angolan border, it is the 'Ngovo Tradition' around 350 BC that shows the arrival of the Neolithic wave of advance.
In Kivu, across the country to the east, the Urewe Tradition villages first appeared about 650 BC. The few archaeological sites known in Congo are a western extension of the Urewe culture which has been found chiefly in Uganda, Rwanda, Burundi and western Kenya and Tanzania. From the start of this tradition, the people knew iron smelting, as is evidenced by several iron-smelting furnaces excavated in Rwanda and Burundi.
The earliest evidence further to the west is known in Cameroon and near to the small town of Bouar in Central Africa. Though further studies are needed to establish a better chronology for the start of iron production in Central Africa, the Cameroonian data places iron smelting north of the Atlantic Equatorial coastal forests around 650 BC to 550 BC. This technology developed independently from the previous Neolithic expansion, some 900 years later. As fieldwork done by a German team shows, the Congo River network was slowly settled by food-producing villagers going upstream in the forest. Work from a Spanish project in the Ituri area further east suggests villages reached there only around 1,150 BC.
The supposedly Bantu-speaking Neolithic and then iron-producing villagers added to and displaced the indigenous Pygmy populations (also known in the region as the "Batwa" or "Twa") into secondary parts of the country. Subsequent migrations from the Darfur and Kordofan regions of Sudan into the north-east, as well as East Africans migrating into the eastern Congo, added to the mix of ethnic groups. The Bantu-speakers imported a mixed economy made up of agriculture, small-stock raising, fishing, fruit collecting, hunting and arboriculture before 3,500 BP; iron-working techniques, possibly from West Africa, a much later addition. The villagers established the Bantu language family as the primary set of tongues for the Congolese.
The process in which the original Upemba society transitioned into the Kingdom of Luba was gradual and complex. This transition ran without interruption, with several distinct societies developing out of the Upemba culture prior to the genesis of the Luba. Each of these kingdoms became very wealthy due mainly to the region's mineral wealth, especially in ores. The civilization began to develop and implement iron and copper technology, in addition to trading in ivory and other goods. The Luba established a strong commercial demand for their metal technologies and were able to institute a long-range commercial net (the business connections extended over 1,500 kilometres (930 miles), all the way to the Indian Ocean). By the 16th century, the kingdom had an established strong central government based on chieftainship. The Eastern regions of the precolonial Congo were heavily disrupted by constant slave raiding, mainly from Arab/Zanzibari slave traders such as the infamous Tippu Tip.