Question: When did the country with the largest economy in Africa become a federation of 19 states?

full_context: Document 1: Mid-Western Region, Nigeria: It was formed in June 1963 from Benin and Delta provinces of the Western Region, and its capital was Benin City. It was renamed a province in 1966, and in 1967 when the other provinces were split up into several states, it remained territorially intact, becoming a state.
Document 2: States of Nigeria: Date Events Map 1960 - 1963 At the time of independence in 1960, Nigeria was a Federal State of three Regions: Northern, Western, and Eastern. Additionally, provinces, which were a legacy of colonial times, remained extant until they were abolished in 1976. 1963 - 1967 In 1963, two provinces were detached from the Western Region to form the new Mid-Western Region. 1967 - 1976 In 1967, the regions were replaced by 12 states due to a military decree; only the former Mid-Western Region escaped division, and formed a single state following the restructuring. From 1967 to 1970 the areas of Mid-Western State and the Eastern Region attempted to secede, as a nation called Biafra during the Nigerian civil war. 1976 - 1987 In 1976, seven new states were created, making 19 altogether. 1987 - 1991 During this period, there were 21 states and later, Abuja, the Federal Capital Territory. 1991 - 1996 During this period, there were 30 states and the Federal Capital Territory. The Federal Capital Territory was established in 1991. In 1987 two new states were established, followed by another nine in 1991, bringing the total to 30. The latest change, in 1996, resulted in the present number of 36 states.
Document 3: Nigeria: Modern-day Nigeria has been the site of numerous kingdoms and tribal states over the millennia. The modern state originated from British colonial rule beginning in the 19th century, and the merging of the Southern Nigeria Protectorate and Northern Nigeria Protectorate in 1914. The British set up administrative and legal structures whilst practising indirect rule through traditional chiefdoms. Nigeria became a formally independent federation in 1960, and plunged into a civil war from 1967 to 1970. It has since alternated between democratically-elected civilian governments and military dictatorships, until it achieved a stable democracy in 1999, with its 2011 presidential elections being viewed as the first to be conducted reasonably freely and fairly.
Document 4: Geopolitical zones of Nigeria: The six geopolitical zones of Nigeria is a major division in modern Nigeria, created during the regime of president General Sani Abacha. Nigerian economic, political and educational resources are often shared across the zones.
Document 5: History of Nigeria: In 1914, the area was formally united as the Colony and Protectorate of Nigeria. Administratively, Nigeria remained divided into the Northern and Southern Provinces and Lagos Colony. Western education and the development of a modern economy proceeded more rapidly in the south than in the north, with consequences felt in Nigeria's political life ever since. Following World War II, in response to the growth of Nigerian nationalism and demands for independence, successive constitutions legislated by the British Government moved Nigeria toward self - government on a representative and increasingly federal basis. On 1 October 1954, the colony became the autonomous Federation of Nigeria. By the middle of the 20th century, the great wave for independence was sweeping across Africa. On 27 October 1958 Britain agreed that Nigeria would become an independent state on 1 October 1960.
Document 6: Nigeria: Nigeria is often referred to as the ``Giant of Africa '', owing to its large population and economy. With 186 million inhabitants, Nigeria is the most populous country in Africa and the seventh most populous country in the world. Nigeria has the third - largest youth population in the world, after India and China, with more than 90 million of its population under age 18. The country is viewed as a multinational state as it is inhabited by over 500 ethnic groups, of which the three largest are the Hausa, Igbo and Yoruba; these ethnic groups speak over 500 different languages and are identified with a wide variety of cultures. The official language is English. Nigeria is divided roughly in half between Christians, who live mostly in the southern part of the country, and Muslims, who live mostly in the north. A minority of the population practise religions indigenous to Nigeria, such as those native to the Igbo and Yoruba ethnicities.
Document 7: Nigeria: According to the International Organization for Migration, Nigeria witnessed a dramatic increase in remittances sent home from overseas Nigerians, going from USD 2.3 billion in 2004 to 17.9 billion in 2007. The United States accounts for the largest portion of official remittances, followed by the United Kingdom, Italy, Canada, Spain and France. On the African continent, Egypt, Equatorial Guinea, Chad, Libya and South Africa are important source countries of remittance flows to Nigeria, while China is the biggest remittance-sending country in Asia.
Document 8: Member states of the Organisation of Islamic Cooperation: Nigeria -- Federal Republic of Nigeria Capital: Abuja A 1986 A 7008178517000000000 ♠ 178,517,000 A 7005923768000000000 ♠ 923,768 A English (hide) Further details Nigeria is a federation of 36 states and 1 federal territory.
Document 9: List of African countries by GDP (PPP): Region Rank Country 2015 GDP (PPP) millions of International dollars -- Africa 5,736,700 Nigeria 1,192.00 Egypt 995.97 South Africa 724.01 Algeria 570.64 Morocco 274.53 6 Angola 185.25 7 Sudan 167.42 8 Ethiopia 159.22 9 Tanzania 150.4 10 Kenya 143.05 11 Tunisia 127.21 12 Ghana 113.35 13 Libya 92.88 14 Uganda 79.75 15 Ivory Coast 78.34 16 Cameroon 72.11 17 Zambia 64.65 18 Democratic Republic of the Congo 63.27 19 Botswana 37.16 20 Senegal 36.30 21 Madagascar 35.56 22 Gabon 34.41 23 Chad 33.73 24 Mozambique 32.00 25 Burkina Faso 31.18 26 Mali 29.15 27 Zimbabwe 28.90 28 Republic of the Congo 27.92 29 Equatorial Guinea 25.94 30 Mauritius 24.84 31 Namibia 24.51 32 Benin 21.16 33 Malawi 20.56 34 Rwanda 20.32 35 Niger 18.96 36 Mauritania 16.43 37 Guinea 15.28 38 Swaziland 10.87 39 Togo 10.82 40 Eritrea 7.94 41 Burundi 7.88 42 Somalia 5.90 43 Lesotho 5.78 44 Gambia 3.27 45 Liberia 3.78 46 Cape Verde 3.48 47 Djibouti 3.09 48 Seychelles 2.53 49 Guinea - Bissau 1.94 50 Central African Republic 1.62 51 Comoros 1.21 52 São Tomé and Príncipe 0.66
Document 10: Nigeria: Nigeria is divided into thirty-six states and one Federal Capital Territory, which are further sub-divided into 774 Local Government Areas (LGAs). The plethora of states, of which there were only three at independence, reflect the country's tumultuous history and the difficulties of managing such a heterogeneous national entity at all levels of government. In some contexts, the states are aggregated into six geopolitical zones: North West, North East, North Central, South East, South South, and South West.
Document 11: Nigeria: As of 2015[update], Nigeria is the world's 20th largest economy, worth more than $500 billion and $1 trillion in terms of nominal GDP and purchasing power parity respectively. It overtook South Africa to become Africa's largest economy in 2014. Also, the debt-to-GDP ratio is only 11 percent, which is 8 percent below the 2012 ratio. Nigeria is considered to be an emerging market by the World Bank; It has been identified as a regional power on the African continent, a middle power in international affairs, and has also been identified as an emerging global power. Nigeria is a member of the MINT group of countries, which are widely seen as the globe's next "BRIC-like" economies. It is also listed among the "Next Eleven" economies set to become among the biggest in the world. Nigeria is a founding member of the Commonwealth of Nations, the African Union, OPEC, and the United Nations amongst other international organisations.
Document 12: Nigeria: Nigeria was ranked 30th in the world in terms of GDP (PPP) in 2012. Nigeria is the United States' largest trading partner in sub-Saharan Africa and supplies a fifth of its oil (11% of oil imports). It has the seventh-largest trade surplus with the US of any country worldwide. Nigeria is the 50th-largest export market for US goods and the 14th-largest exporter of goods to the US. The United States is the country's largest foreign investor. The International Monetary Fund (IMF) projected economic growth of 9% in 2008 and 8.3% in 2009. The IMF further projects an 8% growth in the Nigerian economy in 2011.
Document 13: Federal government of Nigeria: The Federal Government of Nigeria is the federal government for the Federal Republic of Nigeria, a federation in West Africa, composed of 36 states, who share sovereignty with the federal government and 1 federal territory administered solely by the federal government. The federal government is composed of three distinct branches: legislative, executive, and judicial, whose powers are vested by the Constitution of Nigeria in the National Assembly, the President, and the federal courts, including the Supreme Court, respectively.
Document 14: List of African countries by GDP (nominal): 2017 Rank Country Nominal GDP ($billions) Nominal GDP per capita (US $) Notes Nigeria 376.284 1,994.235 South Africa 349.299 6,179.870 Egypt 237.037 2,500.772 Algeria 178.287 4,292.272 Angola 124.209 4,407.657 6 Sudan 119.00 1,428.000 7 Morocco 109.824 3,151.145 8 Ethiopia 80.874 872.840 9 Kenya 79.511 1,701.550 10 Tanzania 51.725 1,033.567 11 Ghana 47.032 1,663.190 12 Democratic Republic of the Congo 41.441 478.237 13 Ivory Coast 40.360 1,616.981 14 Tunisia 40.275 3,496.286 15 Cameroon 34.006 1,400.743 16 Libya 31.331 4,858.672 17 Uganda 26.349 699.410 18 Zambia 25.504 1,479.542 19 Zimbabwe 17.491 1,175.723 20 Botswana 17.168 7,876.997 21 Senegal 16.463 1,038.094 22 Mali 15.318 810.771 23 Gabon 15.206 7,971.589 24 Namibia 12.687 5,413.508 25 Mozambique 12.681 429.296 26 Burkina Faso 12.569 663.806 27 Mauritius 12.428 9,794.102 28 Madagascar 11.463 447.558 29 Equatorial Guinea 10.725 12,726.956 30 Chad 9.872 810.163 31 Guinea 9.721 749.463 32 Benin 9.238 830.404 33 Rwanda 9.137 771.702 34 Congo 8.513 1,958.174 35 Niger 8.253 439.997 36 Somalia 7.382 547.32 37 Malawi 6.206 323.740 38 Eritrea 5.813 979.692 39 Mauritania 5.116 1,317.938 40 Togo 4.767 611.133 41 Swaziland 4.491 3,914.821 42 Sierra Leone 3.641 491.448 43 Burundi 3.396 312.463 44 Liberia 3.285 729.292 45 South Sudan 2.870 228.034 46 Lesotho 2.768 1,425.310 47 Djibouti 2.029 1,988.765 48 Central African Republic 1.928 386.806 49 Cape Verde 1.741 3,237.597 50 Seychelles 1.482 15,685.955 51 Guinea - Bissau 1.350 794.107 52 The Gambia 1.009 480.040 53 Comoros 0.652 787.831 54 São Tomé and Príncipe 0.379 1,785.280 -- Total 2,191.104
Document 15: Nigeria: Nigeria is often referred to as the "Giant of Africa", owing to its large population and economy. With approximately 182 million inhabitants, Nigeria is the most populous country in Africa and the seventh most populous country in the world. Nigeria has one of the largest populations of youth in the world. The country is viewed as a multinational state, as it is inhabited by over 500 ethnic groups, of which the three largest are the Hausa, Igbo and Yoruba; these ethnic groups speak over 500 different languages, and are identified with wide variety of cultures. The official language is English. Nigeria is divided roughly in half between Christians, who live mostly in the southern part of the country, and Muslims in the northern part. A minority of the population practise religions indigenous to Nigeria, such as those native to Igbo and Yoruba peoples.
ground_truth: 1976
sub_queries: What is the largest economy in Africa? Answer: Nigeria
when did Nigeria become a federation of 19 states Answer: 1976