When historians refer to Africa in premodern times, they are speaking generally of a geographic concept, a continental landmass, and not a cultural identity. Certainly few, if any, people living on the continent at that time thought of themselves as Africans. Like Eurasia or the Americas, Africa hosted numerous separate societies, cultures, and civilizations with vast differences among them as well as some interaction between them.

Many of these differences grew out of the continent’s environmental variations. Small regions of Mediterranean climate in the northern and southern extremes, large deserts (the Sahara and the Kalahari), even larger regions of savanna grasslands, tropical rain forest in the continent’s center, highlands and mountains in eastern Africa—all of these features, combined with the continent’s enormous size, ensured endless variation among Africa’s many peoples. Africa did, however, have one distinctive environmental feature: bisected by the equator, it was the most tropical of the world’s three supercontinents. Persistent warm temperatures caused the rapid decomposition of vegetable matter called humus, resulting in poorer and less fertile soils and a less productive agriculture than in the more temperate Eurasia. Those climatic conditions also spawned numerous disease-carrying insects and parasites, which have long created serious health problems in many parts of the continent. It was within these environmental constraints that African peoples made their histories. In several distinct regions of the continent—the upper Nile valley, northern Ethiopia/Eritrea, and the Niger River valley—small civilizations flourished during the second-wave era, while others followed later.