For 10 points, name this longest river of West Africa, the namesake of two countries in the region.
One tributary of this river rises in the Adamawa Plateau and flows through Lagdo Reservoir before joining this river at Lokoja. A tributary of this river flows by the city of SÃ©gou, which served as the capital of the 18th century Bambara Empire. That tributary is the Benue. The exploitation of oil reserves on this river has caused the rise of militant groups such as MEND. The first Westerner to reach the central section of this river was the Scottish explorer Mungo Park. This river empties into the Gulf of Guinea after flowing through Bamako, Timbuktu, and Niamey. For 10 points, name this longest river of West Africa, the namesake of two countries in the region.
One tributary of this river rises in the Adamawa Plateau and flows through Lagdo Reservoir before joining this river at Lokoja.
Niger River [or fleuve Niger; or Joliba; or Isa Ber; or Oya; or Kwara]