Final answer:
Askia the Great challenged Sunni Ali's legitimacy by positioning himself as a devout Muslim leader, receiving recognition from the caliph of Egypt, and centralizing power through the appointment of loyal governors, thereby solidifying his rule and starting the Askia dynasty.
Step-by-step explanation:
Askia the Great, also known as Askia Muhammad, challenged Sunni Ali's legitimacy and established his own rule by leveraging various strategies. Following the death of Sunni Ali in 1492, his son, Sonni Baru, ascended to the throne, but his rule was short-lived as Muhammad Ture (Askia Muhammad) contested his rule. In battle, Sonni Baru was defeated by Muhammad Ture in April 1493, leading to Muhammad Ture's rise to power as Askia the Great and the beginning of the Askia dynasty.
Critically, Sunni Ali had been criticized by Arabic historians for his harsh measures against Islamic scholars and his lack of respect for Islam. The discontent among Muslims provided fertile ground for Askia Muhammad to establish his legitimacy on the basis of religious authority. In contrast to Sunni Ali's approach, Askia the Great elevated the standing of Islam in the Songhai Empire by declaring a holy war against the non-Muslim Mossi and by conducting a pilgrimage to Mecca, where he received recognition from the caliph of Egypt.
Moreover, Askia the Great reformed the governmental structure by appointing royal family members or trusted servants as provincial governors, replacing the traditional rulers. This centralization of power and alignment with Islam strengthened his legitimacy and drastically reduced the risk of provinces asserting their independence during dynastic struggles.