Songhai Empire: West African State
1009-1592 AD
Vogel, Joseph O., Encyclopedia of Precolonial Africa: Archaeology, History, Languages, Cultures, and Environments, (1997) pp. 493-494:

In 1009 AD, King Kossoi of Gao accepted Islam, probably under the influence of merchants or scholars who preceded the Almoravid incursions in the area. Basil Davidson argues that to the African kings of the time, Islam was probably equated with commerce. Islam also provided a unifying structure that crossed tribal gods and ancestor beliefs. At this time, the capital was established at Gao. Songhai then became a tributary state to the kingdom of Mali from 1325 to 1335. Ali Kohlen was the brother who restored freedom to the Songhai. Little is known of the next century other than that it was probably a time of struggle for the Songhai, who were constantly fighting off neighbors: the Tuareg, the Mossi, and the Mandingo.

In 1464, Sonni Ali ascended the throne of Songhai. He was the 18th ruler in the line of kings founded by Kossoi in 1009. In 1468, he captured Timbuktu and took Jenne-jeno by 1473, and by his death in 1492, he had established a fairly stable area over much of the Middle and Upper Niger. He was succeeded by his son, who only lasted a few months before one of Sonni Ali's generals, with popular support, usurped the crown. This general, Mohammed Toure, was a Muslim, and he became known as Askia Mohammed. His main strength was organization, and he proceeded to divide the state into administered provinces, each with its own governor, often a member of his own family.
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He created central offices to administer financial, agricultural, and other matters and instituted a tax system. He made all weights and measures uniform within his domain. He was sympathetic to Muslim  and encouraged their work. Once again Timbuktu, Jenne-jeno, and Walata flourished as centers of learning and religion. The University of Timbuktu was one of the first in Africa and drew scholars from all over the Muslim world. Trade was based on gold and salt primarily but also included ivory, ebony, kola nuts, cotton goods, grains, and ostrich feathers. From the north, imported goods included horses, North African and European luxury items, weapons (sword blades came from as far away as Spain and Germany), and cowrie shells. The absence of local salt and the need to import it from Taghaza more than 800 kilometers away is mentioned by Leo Africanus.

Askia Mohammed, too, made a pilgrimage to Mecca, arriving there in 1497. He is said to have given 10,000 gold pieces as alms to the poor and for the establishment and upkeep of a hostel for other pilgrims from the western Sudan. When he returned, he continued the expansion of the state and eventually took all land that had once belonged to Mali. He then attacked the Hausa states to the east, and by 1515, he had successfully defeated the Tuareg and taken their stronghold at Agadez in the Air region. This gave him control over the trade routes leading to Tunis, Tripoli, and Egypt. Askia Mohammed created the largest African state in the western Sudan. It was well administered and probably the most organized of the African states. In addition, with Muslim support, trade, culture, scholarly activities, and religion flourished as never before. Leo Africanus noted that numerous judges, doctors, and clerics in Timbuktu received salaries from the ruler, who was reputed to respect men of learning. Since there was a rich market for books in manuscript, profit was made from the book trade as well.

Songhai continued to flourish, even though Askia Mohammed was deposed by his son in 1528, and there ensued a series of struggles for the crown. Morocco, however, had long been envious of the power of the Songhai, and in 1589, El Mansur set out to attack the Songhai Empire. None of his advisors thought it would be possible to cross the Sahara with an army and all the supplies that would necessarily have to accompany it. A Spaniard, named Judar, was chosen as commander over an army of 4,000 soldiers, mostly Europeans with a few Moroccans. Accompanying the troops were some 9,000 transport animals. It took approximately six months to cross the desert, and news of the army's progress was reported to the Songhai king by travelers. The king, Askia Ishak, faced the Moroccan army at Tondibi, 56 kilometers from Gao, with an army composed of 18,000 cavalry and 9,000 infantry. Judar's army had been reduced to 1,000 men during the arduous desert crossing. But the Moroccans had guns, which the Songhai did not, and given the advantage of gunpowder and firearms over the simple weapons of the Songhai, it is not surprising that Judar won without difficulty. In spite of this victory, a Moroccan province was never established. Songhai resistance continued into the early decades of the 17th century, and disease, particularly malaria and dysentery, took its toll on the mostly European mercenaries fighting for Morocco. The region fragmented into many smaller states and chiefdoms. The cities retained a more international flavor but gradually declined in importance as the trans-Atlantic trade grew.
In Pop Culture:

Askia Mohammed I appears as the leader of the Songhai Empire in the multi-award winning computer game Civilization V.

The tomb of Askia Mohammed I. Built at the end of the 15th century, at Gao in Mali.