A loose confederation of Yoruba kingdoms in West Africa. By the early 19th century the Yoruba empire of Oyo was beginning to disintegrate, a process accelerated by the decline of the slave trade and the rise of the Fulani empire in the north. The Fulani destroyed the old city of Oyo, creating the Muslim emirate of Ilorin. Alafin Atiba, the new ruler of the Oyo empire (1836–59), built a capital, Ago Oja, and allied his empire with Ibadan, but on his death civil war developed. At the same time the influence of the spiritual leader of the Yoruba people, the Oni of Ife, began to decline with the arrival of Christian missionaries. In 1888 a treaty was made with the then Alafin of Oyo, whereby all the Yoruba kingdoms were brought under British protection. In 1900 the empire was incorporated into the protectorate of Southern Nigeria.