stylistic:tone, structural:reformatting
Adamawa State is a state in the North-East geopolitical zone of Nigeria, bordered by Borno to the northwest, Gombe to the west, and Taraba to the southwest while its eastern border forms part of the national border with Cameroon. It takes its name from the historic emirate of Adamawa, with the emirate's old capital of Yola serving as the capital city of Adamawa State. The state was formed in 1991 when the former Gongola State was broken up into Adamawa and Taraba states. The state is one of the most heterogeneous in Nigeria, having over 100 indigenous ethnic groups. Of the 36 states, Adamawa is the eighth largest in area, but the thirteenth least populous with an estimated population of about 4.25 million as of 2016. Geographically, the state is mainly composed of highlands and mountains and the Adamawa Plateau crossed by valleys and rivers, most notably the Benue and Gongola rivers. The lowlands of Adamawa are part of the West Sudanian savanna in the north and the wetter Guinean forest–savanna mosaic in parts of the south, while elevated areas are parts of the Mandara Plateau mosaic and Cameroonian Highlands forests ecoregions. In the extreme south of the state is part of the Gashaka Gumti National Park, a large wildlife park that contains large populations of bushbuck, African buffalo, patas monkey, black-and-white colobus, giant pangolin, and hippopotamus along with some of Nigeria's last remaining Nigeria-Cameroon chimpanzee, African leopard, and African golden cat populations. What is now known as Adamawa state has been inhabited for years by various ethnic groups, including the Bwatiye (Bachama), Bali, Bata (Gbwata), Gudu, Mbula-Bwazza, and Nungurab (Lunguda) in the central region; the Kamwe in the north and central region; the Jibu in the far south; the Kilba, Mafa, Marghi, and Waga in the north, and the Mumuye in the south while the Fulani live throughout the state — often as nomadic herders. Adamawa is also religiously diverse as about 50% of the population is Sunni Muslim and 40% is Christian, while the remaining 10% are adherents of traditional ethnic religions. As an agriculturally-based state, the Adamawa State economy mainly relies on livestock and crops, such as cotton, groundnuts, millet, cassava, guinea corn, and yams. Due to the Boko Haram insurgency affecting development in the state, Adamawa has the eleventh lowest Human Development Index in the country but as the insurgency has abated since 2016 due to terrorist infighting, development has been renewed.