Between the 9th and 15th centuries, Bantu-speaking states began to emerge in the Great Lakes region and in the savannah south of the Central African rain forest. On the Zambezi river, the Monomatapa kings built the Great Zimbabwe complex, a civilisation ancestral to the Kalanga people.[19] Comparable sites in Southern Africa, include Bumbusi in Zimbabwe and Manyikeni in Mozambique.
From the 12th century onward, the processes of state formation amongst Bantu peoples increased in frequency. This was probably due to denser population (which led to more specialized divisions of labor, including military power, while making emigration more difficult); to technological developments in economic activity; and to new techniques in the political-spiritual ritualization of royalty as the source of national strength and health.[20] Some examples of such Bantu states include: in Central Africa, the Kingdom of Kongo, the Kuba Kingdom, the Lunda Empire, the Luba Empire, Tooro, Bunyoro, Buganda, Busoga, Rwanda, Burundi, Ankole and in Southern Africa, the Mutapa Empire, the Zulu Kingdom, the Ndebele Kingdom, Mapungubwe, the Kingdom of Butua, Maravi, Danamombe, Khami, Naletale, Kingdom of Zimbabwe[21] and the Rozwi Empire.[22]

On the coastal section of East Africa, a mixed Bantu community developed through contact with Muslim Arab and Persian traders, Zanzibar being an important part in the Arab slave trade. The Swahili culture that emerged from these exchanges evinces many Arab and Islamic influences not seen in traditional Bantu culture, as do the many Afro-Arab members of the Bantu Swahili people. With its original speech community centered on the coastal parts of Zanzibar, Kenya, and Tanzania – a seaboard referred to as the Swahili Coast – the Bantu Swahili language contains many Arabic loan-words as a result of these interactions.[23] The Arab slave trade also brought Bantu influence to Madagascar,[24] the Malagasy people showing Bantu admixture, and their Malagasy language Bantu loans.[25] Toward the 18th and 19th centuries, the flow of Zanj (Bantu) slaves from Southeast Africa increased with the rise of the Omani Sultanate of Zanzibar, based in Zanzibar, Tanzania. With the arrival of European colonialists, the Zanzibar Sultanate came into direct trade conflict and competition with Portuguese and other Europeans along the Swahili Coast, leading eventually to the fall of the Sultanate and the end of slave trading on the Swahili Coast in the mid-20th century.