<P> Following the breakup of Mali, a local leader named Sonni Ali (1464--1492) founded the Songhai Empire in the region of middle Niger and the western Sudan and took control of the trans - Saharan trade . Sonni Ali seized Timbuktu in 1468 and Jenne in 1473, building his regime on trade revenues and the cooperation of Muslim merchants . His successor Askia Mohammad I (1493--1528) made Islam the official religion, built mosques, and brought to Gao Muslim scholars, including al - Maghili (d. 1504), the founder of an important tradition of Sudanic African Muslim scholarship . By the eleventh century, some Hausa states--such as Kano, jigawa, Katsina, and Gobir--had developed into walled towns engaging in trade, servicing caravans, and the manufacture of goods . Until the fifteenth century, these small states were on the periphery of the major Sudanic empires of the era, paying tribute to Songhai to the west and Kanem - Borno to the east . </P> <P> Slavery had long been practised in Africa . Between the 7th and 20th centuries, Arab slave trade (also known as slavery in the East) took 18 million slaves from Africa via trans - Saharan and Indian Ocean routes . Between the 15th and the 19th centuries (500 years), the Atlantic slave trade took an estimated 7--12 million slaves to the New World . More than 1 million Europeans were captured by Barbary pirates and sold as slaves in North Africa between the 16th and 19th centuries . </P> <P> In West Africa, the decline of the Atlantic slave trade in the 1820s caused dramatic economic shifts in local polities . The gradual decline of slave - trading, prompted by a lack of demand for slaves in the New World, increasing anti-slavery legislation in Europe and America, and the British Royal Navy's increasing presence off the West African coast, obliged African states to adopt new economies . Between 1808 and 1860, the British West Africa Squadron seized approximately 1,600 slave ships and freed 150,000 Africans who were aboard . </P> <P> Action was also taken against African leaders who refused to agree to British treaties to outlaw the trade, for example against "the usurping King of Lagos", deposed in 1851 . Anti-slavery treaties were signed with over 50 African rulers . The largest powers of West Africa (the Asante Confederacy, the Kingdom of Dahomey, and the Oyo Empire) adopted different ways of adapting to the shift . Asante and Dahomey concentrated on the development of "legitimate commerce" in the form of palm oil, cocoa, timber and gold, forming the bedrock of West Africa's modern export trade . The Oyo Empire, unable to adapt, collapsed into civil wars . </P>

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