Lust For Gold
When the Portuguese first sailed down the Atlantic coast of Africa in the 1430's, they were interested in one thing. Surprisingly, given modern perspectives, it was not slaves but gold. Ever since Mansa Musa, the king of Mali, made his pilgrimage to Mecca in 1325, with 500 slaves and 100 camels (each carrying gold) the region had become synonymous with such wealth. There was one major problem: trade from sub-Saharan Africa was controlled by the Islamic Empire which stretched along Africa's northern coast. Muslim trade routes across the Sahara, which had existed for centuries, involved salt, kola, textiles, fish, grain, and slaves.
As the Portuguese extended their influence around the coast, Mauritania, Senagambia (by 1445) and Guinea, they created trading posts. Rather than becoming direct competitors to the Muslim merchants, the expanding market opportunities in Europe and the Mediterranean resulted in increased trade across the Sahara. In addition, the Portuguese merchants gained access to the interior via the Senegal and Gambia rivers which bisected long-standing trans-Saharan routes.
Beginning to Trade
The Portuguese brought in copper ware, cloth, tools, wine and horses. (Trade goods soon included arms and ammunition.) In exchange, the Portuguese received gold (transported from mines of the Akan deposits), pepper (a trade which lasted until Vasco da Gama reached India in 1498) and ivory.
Shipping Slaves for the Islamic Market
There was a very small market for African slaves as domestic workers in Europe, and as workers on the sugar plantations of the Mediterranean. However, the Portuguese found they could make considerable amounts of gold transporting slaves from one trading post to another, along the Atlantic coast of Africa. Muslim merchants had an insatiable appetite for slaves, which were used as porters on the trans-Saharan routes (with a high mortality rate), and for sale in the Islamic Empire.