<Li> The Nok Civilization is considered to be one of the most advanced ancient sub-Saharan civilizations in African history . Beginning some time around 1500 BC, it was largely concentrated in what is now Nigeria but produced some of the first sub-Saharan iron smelting and terracotta architecture . Mysteriously died out around 200 AD . </Li> <Li> The Kingdom of Nri (1043--1911) was the West African medieval state of the Nri - Igbo, a subgroup of the Igbo people, and is the oldest kingdom in Nigeria . The Kingdom of Nri was unusual in the history of world government in that its leader exercised no military power over his subjects . The kingdom existed as a sphere of religious and political influence over much of Igboland, and was administered by a priest - king called the eze Nri . The eze Nri managed trade and diplomacy on behalf of the Igbo people, and was the possessor of divine authority in religious matters . </Li> <Li> The Oyo Empire (1400--1895) was a West African empire of what is today western Nigeria . The empire was established by the Yoruba in the 15th century and grew to become one of the largest West African states . It rose to prominence through wealth gained from trade and its possession of a powerful cavalry . The Oyo Empire was the most politically important state in the region from the mid-17th to the late 18th century, holding sway not only over other Yoruba states, but also over the Fon kingdom of Dahomey (located in the state now known as the Republic of Benin). </Li> <Li> Benin Empire (1440--1897), a pre-colonial African state of modern Nigeria . </Li>

Which of the three west african kingdoms was the largest