Excerpts from Books and Wikipedia
"For centuries Arabians, Indonesians, Persians, and Indians had traded with the coastal communities of East Africa. By the 13th century, Arabs dominated eastern African trade, and evolved the Swahili city states, which grew wealthy on trade in ivory, gold, hides, and slaves. When the Portuguese arrived in 1497, the Swahili cities refused to accept their control. The Portuguese attacked the towns and forcibly subjugated the inhabitants, breaking the Islamic monopoly on trade in the region. They built fortresses at Sofala, Mozambique, Kilwa, and Mombasa. Fort Jesus, at Mombasa, was the Portuguese power base throughout the 17th century." [DK Timelines, p. 290]