When the Portuguese began trading on the west coast of Africa in the 15th century, they concentrated their energies on Guinea and Angola. Hoping at first for gold, they soon found that slaves were the most valuable commodity available in the region for export. The Islamic Empire was already well-established in the African slave trade, for centuries linking it to the Arab slave trade. However, the Portuguese who had conquered the Islamic port of Ceuta in 1415 and several other towns in current day Morocco in a Crusade against Islamic neighbors, managed to successfully establish themselves in the area. But the Portuguese never established much more than a foothold in either place.