The collapse of the Oyo Empire was caused by internal and external crises. The empire faced several challenges including frequent wars with neighboring kingdoms, the rise of powerful provincial leaders, and the emergence of new trade routes that bypassed Oyo. These factors weakened the empire and contributed to its eventual collapse in the early 19th century. While the revolt of Afonja and the British presence in Yorubaland were significant events in the decline of the empire, they were not the primary causes of its collapse.