Nigeria

Nigeria’s most populous city is Lagos, with a population of 15.388 million.

An excerpt from the article 19 facts about Nigeria

Founded by the Portuguese in the late 15th century, the city was Nigeria’s capital from 1960 to 1991. From the 17th to 19th centuries, Lagos was one of the major slave export points. Today it is one of the world’s fastest-growing metropolises, a city that is home to the country’s largest seaport, and Makoko, the world’s fastest slum (floating slum).

In 1975, the Economic Community of West African States was established in Lagos.