Excerpts from Books and Wikipedia
"The Portuguese arrived at the mouth of the Zaire River in the 1480s, and established contact with the kingdom of Kongo (present-day Zaire). As a result of Portuguese missionary activity, the local king adopted the name Alfonso I (1506-43) and embraced Christianity, promoting it as a royal religious cult, and made efforts to westernize his kingdom. When Kongo was attacked by nomadic warriors, known as the Jaga, in 1568, the Portuguese came to Kongo's aid, providing the military support needed to drive them out. But Kongo was now a client state of Portuguese traders. In 1571, King Alvaro I was installed on the throne by the Portuguese. He became increasingly dependent on Portuguese military aid, which he paid for by exporting captives for the Atlantic slave trade. As the demand for slaves grew in the 17th century, the king's authority collapsed and Kongo disintegrated into rival factions." [DK Timelines, p. 291]