The movement of the Kusi Bantu across the eastern and southern parts of Africa spread a variety of agricultural practices, as well as the Bantu languages.

Between 400 b.c.e. and 300 c.e., a process of population relocation was under way in southern and south-central Africa, initiated by Bantu communities. This population movement and resettlement was a continuation of the expansion of Bantu communities within eastern Africa beginning around 1000 b.c.e. Several factors contributed to these demographic shifts among the Bantu-speaking communities, in both eastern and southern Africa. The most significant and ecologically visible dynamic spurring migration was a prolonged population growth. Large demographic increases for an extended period of time over several centuries likely threatened the stability of the food supply in the western parts of East Africa, ultimately leading to the expansion of Bantu populations out of eastern Africa and into southern Africa.

Speakers of non-Bantu languages with hunting-and-gathering economies were the primary inhabitants of southern Africa until the latter part of the last millennium b.c.e., when the Bantu agriculturalists began to emerge. The primary inhabitants of southern Africa before the Bantu arrival spoke ancestral Khoikhoi languages, which are related to the few remaining Khoisan languages of modern-day southern Africa. In contrast to the strictly hunting-and-gathering lifestyle of the semidesert-dwelling populations of southern Africa, the earliest Bantu had combined hunting and gathering with root-crop agriculture in the tropical forests of western and central Africa, and their descendants continued this system of food production with some modifications.

By the last millennium b.c.e., the Bantu agriculturalists of western Africa were, like their later eastern African counterparts, faced with growing populations requiring intensified production. The intensification of cultivation in western and eastern Africa resulted in a need for more land on which to grow crops; however, the same land was also in progressively greater demand for settlement by the increasing populations. The food supply was steadily enhanced in quantity and variety, but intensification of cultivation meant there was greater pressure on the land as a resource. The option chosen by some segments of the Bantu in eastern Africa was to relocate away from the western side of East Africa. Thus, a population expansion and migration into far eastern and southern Africa was well under way by the fifth century b.c.e. Settlement was expanded through many parts of the forest and to the edges of woodland savannas to the south and east.

In the east, the non-Bantu Sahelians, who were already well established, introduced to the Bantu speakers both grain cultivation and the domestication of animals such as sheep and cattle. The spread of Bantu populations into southern Africa was greatly facilitated by the introduction of grain crops. Unlike root crops, which require relatively high rainfall levels or irrigation for each plant, grains such as sorghum and certain millets grow well in dry environments. The southern and eastern parts of Africa, which were too dry for traditional forest crops, were perfectly suitable for grains. Thus the Bantu incorporated new economic practices from eastern Sahelian grain cultivators and turned again to migration as a means of alleviating population pressures and resource competition within the western Great Lakes region of East Africa. In some areas of eastern Africa, the eastern Sahelian speakers and Bantu had extensive social contact; in the case of the central Sudanic and Sog peoples, many began to be assimilated into Bantu-speaking communities.

The most commonly followed routes of migration must have been through the generally tsetse-free corridors of East Africa, which extend south and southeast of modern-day Tanzania from the Rungwe Mountains along the western side of the Lwangwa River Valley to the Batoka Plateau of southern Zambia. The Mashariki Bantu spread farther east and into the south across East Africa into the regions known today as Uganda, Kenya, and Tanzania. Other Bantu peoples, known to scholars as Kusi Bantu, spread directly south from the savanna into areas of southern Zaire and into modern Angola, Zambia, Mozambique, Zimbabwe, and South Africa. In the southern regions, the Kusi Bantu encountered Khoisan-speaking peoples who engaged predominantly in hunting-and-gathering economies.

A complex of crops allowed for settlement in a greater variety of regions, and the increase in both quality and quantity of food production continued the trend of Bantu population growth. The smelting of iron allowed production of tools such as axes, hoes, arrows, spears, and knives, which, scholars conclude, facilitated movement into a diversity of environments in which new communities could be pioneered. The introduction of luxury goods, as well as new apparatuses and technologies of food production, made trade with neighboring communities attractive. New tools made from iron alleviated the difficulties of acquiring the heavily demanded firewood for cooking, pottery making, and ultimately more iron smelting. Iron production allowed for the making of equipment and tools more durable than their stone or wooden counterparts. In the dry regions of eastern and southern Africa, where grain was typically grown, there were not many forested areas to be continuously cut down for wooden tool production. Iron could be smelted in forested areas at local smelting sites, and then the iron that was produced could be carried back to the more distant settlements in savanna and nonforested areas.

The spread of Bantu populations over most of southern and eastern Africa spread Bantu languages through eastern and southern Africa, which has had a tremendous impact on the linguistic landscape even into present times. Over centuries, Bantu-speaking communities seem to have absorbed speakers of Khoikhoi languages and reduced the number of descendant Khoisan-speaking communities. In the twenty-first century, more than one-third of the African continent speaks Bantu languages because of the large area over which the Bantu spread, although in most previously Khoikhoi-speaking regions there are some Khoisan root words and linguistic features, such as clicks, which have been preserved through incorporation into the Bantu languages.

The concept of grain cultivation moved with the Bantu into areas that were once habitable only by hunters and gatherers because few known indigenous plants could be domesticated and cultivated as staple crops in these areas of southern Africa. The Bantu can be credited with introducing cultivated grains and cattle raising, two new subsistence practices, to a variety of areas within Africa, particularly in the arid south and east. Because domestic animals reproduce more rapidly and frequently than humans, cattle raising, along with grain production, created a secure supply of foodstuffs. With increased agriculture in southern Africa came the opportunity for villages and town centers to develop, as people were typically drawn to the new agricultural areas. Before the arrival of Bantu agriculturalists, the population density of the indigenous Khoisan across southern Africa was low. The expansion of the Bantu therefore was characteristically rapid, because there was a very modest population to deter Bantu establishment of settlements in many areas.

The use of iron was expanded into new regions as the cultivation of grain was spread with Bantu population movement. This dispersion of technology led to increased modifications of iron smelting and smithing within southern Africa. Social and economic changes emerged as different groups of people spread and lost their connections to other Bantu communities from which they had diverged geographically and culturally. Some of the cultural changes included a shift from a double-descent system (wherein matriclans, matrilineage, and patrilineages were significant) to a system wherein such bilateral lineage connections became irrelevant. In southern Africa, either matrilineages were central or, in a few select locations, patrilineages became the principal unit of social organization. In some areas of southern Africa, the distribution of iron wealth gave rise to communities in which clan became more important than lineage in social precedence.

• Collins, Robert O., ed. Problems in African History: The Precolonial Centuries. New York: Markus Wiener, 1991. A synthesis of major issues in early African history. One chapter of this book provides an overview of the changes that took place as a result of the Bantu population movements and how they impacted other African peoples.
• Ehret, Christopher. An African Classical Age: Eastern and Southern Africa in World History, 1000 b.c. to a.d. 400. Charlottesville: University Press of Virginia, 1998. Includes an outline as well as a detailed historical and social account of the population movements among Bantu peoples in eastern and southern Africa between 1000 b.c.e. and 400 c.e., based primarily on linguistic evidence.