Nigeria, officially the Federal Republic of Nigeria, is a federal constitutional republic comprising 36 states and its Federal Capital Territory, Abuja. The country is located in West Africa and shares land borders with the Republic of Benin in the west, Chad and Cameroon in the east, and Niger in the north. Its coast in the south lies on the Gulf of Guinea on the Atlantic Ocean. There are over 500 ethnic groups in Nigeria, of which the three largest are the Hausa, Igbo and Yoruba. The British colonised Nigeria in the late nineteenth and early twentieth century, setting up administrative structures and law while recognising traditional chiefs. Nigeria became independent in 1960. Several years later, it had civil war as Biafra tried to establish independence. Military governments in times of crisis have alternated with democratically elected governments. Nigeria is roughly divided in half between Christians, who mostly live in the South and central parts of the country, and Muslims, concentrated mostly in the north. A minority of the population practice traditional and local religions, including the Igbo and Yoruba religions. Nigeria, known as "the Giant of Africa", is the most populous country in Africa and the seventh most populous country in the world. Its oil reserves have brought great revenues to the country. Nigeria is considered to be an Emerging market nation by the World Bank. Nigeria's economy is the second largest in Africa, and the 37th largest in the world as of currently. Nigeria has been identified as a regional power, it also has regional hegemony, and major influence within its region. It is listed among the "Next Eleven" economies. Nigeria is expected to become the largest economy in Africa overtaking South Africa in the near future and become one of the world's Top 20 economies by 2050. Nigeria is a member of both the Commonwealth of Nations, and the African Union.