 The Mali Empire continued to flourish for several centuries, most particularly under Sundiata's grandnephew Musa I, before a succession of weak rulers led to its collapse under Mossi, Tuareg and Songhai invaders.In the 15th century, the Songhai would form a new dominant state based on Gao, in the Songhai Empire, under the leadership of Sonni Ali and Askia Mohammed.Meanwhile, south of the Sudan, strong city-states arose in Igboland, such as the 10th-century Kingdom of Nri, which helped birth the arts and customs of the Igbo people, Bono in the 12th century, which eventually culminated in the formation the all-powerful Akan Empire of Ashanti, while Ife rose to prominence around the 14th century.