From the Senegambia in the west to Cameroon in the east lies a belt of dense tropical rainforest more than 200 miles wide through which short but deep rivers flow to the sea. Several of these rivers make up the maze of the Niger delta known collectively as the oil rivers. Others, such as the Bandama, Volta, Ouémé, and Benin, reach the beaches that extend, with few exceptions, in an unbroken line of coast pounded by heavy surf and laced by an intricate series of lagoons beyond and parallel to the long stretches of sand. Behind the lagoons looms the West African forest that appears from the shore an impenetrable wall into the interior except for the funnel of savanna, the Dahomey Gap, a north–south corridor from the grasslands of the bilad al-sudan to the coast of the Bight of Benin that facilitated the flow of people and trade from the interior to the coast. This rainforest is the creation of heavy annual rainfall (50–80 inches) in two seasons, April to July and September to November, when the southwest monsoons sweep out of the South Atlantic Ocean.

In the centuries following the turn of the first millennium, some of the continent's most sophisticated states emerged from the dense undergrowth of the West African forest. Although these kingdoms never approached the size of their northern neighbors in the savanna and Sahel of the Western Sudan, gold, cola nuts, and slaves from their forests were crucial commodities in the chain of commerce that stretched north to the great empires of the plains and across the Sahara to the Mediterranean. When the trade coming south from the desert could no longer compete with the new, attractive, and sought-after goods easily acquired in trade from the European sea merchants, these forest states flourished due to their proximity to the European trading enclaves of the West African coast. Many of these states were small principalities, but there were others that rivaled in organization and power the empires of the plains; among them, however, lived numerous communities that eschewed the centralized authority that characterized their neighbors. This complex mosaic of states and stateless societies of different ethnicities and political and social complexions perhaps can best be understood by representative examples to illustrate the challenges, interactions, and responses to life in the West African rainforest by its peoples.