From 1100–1400, major African civilizations blossomed around the Niger River. Europeans appeared in the 15th and 16th centuries and established the slave trade. By the end of the 19th century, the British colonized the coastal areas, began to penetrate inland, and established a protectorate over Northern Nigeria by 1900. The British controlled Nigeria through a divide-and-rule method, pitting the various ethnic groups against each other. In the south, the British introduced Christianity, primarily to the Ibo.
After a half century of British rule, Nigeria became fully independent on 1 October 1960. It became a federal republic in 1963 with the country divided into three states based on ethnicities: the Northern Region, the Western Region, and the Eastern Region. During the 1960s, leaders of the different states threatened secession from the federation. By 1966, the First Republic ended with a military coup. Subsequently, the Eastern Region declared its independence as the Republic of Biafra. In the ensuing civil war, the federal government blockaded Biafra and sent troops to reunite the country by force. During the three-year civil war, an estimated two million people died from mass starvation, mostly Christian Ibos.
When the civil war ended in 1970, Major General Yakubu Gowan created a federal system consisting of 12 states and emphasized national reconciliation. Gowan was aided by new public works projects carried out by the central government's revenues from the oil boom. In July 1975, Gowan was overthrown by Brigadier Murtala Muhammad who, in turn, was assassinated on 13 February 1976. Muhammad's chief of staff, Lieutenant General Olusegun Obasanjo became the next head of state. As leader of the Supreme Military Council (SMC), Obasanjo oversaw the drafting of a new Constitution by the National Constituent Assembly and the termination of a 12-year state of emergency. Obasanjo also legalized political parties and paved the way for democratic elections in 1979 and the inauguration of the Second Republic under Alhaji Shagari.
On 31 December 1983, a bloodless coup led by Obasanjo's followers displaced Shagari, who had been democratically reelected in 1983. The military officers seized power, citing increased corruption and economic mismanagement. Led by Major General Ibrahim Babangida, Nigeria's military repeatedly postponed deadlines for return to civilian rule and repressed political opponents and curtailed civil liberties. In September 1987, Babangida announced a five-year plan for return to civilian rule. Elections for the Third Republic were finally held on 12 June 1993, amid rioting and intercommunal violence.
Mashood Abiola, a Yoruba businessman, was widely viewed as the winner of the 1993 elections, but the government never released the election results and instead annulled the results. Babangida refused to relinquish power but later resigned after naming Ernest Shonekan as interim head of state. In November 1993, General Sani Abacha assumed power and dissolved the National Assembly after a military coup. Despite pledges for civilian rule, Abacha increased his repression of political dissidents and inaugurated himself president in July 1994. Subsequently, Abiola was imprisoned. Abacha consolidated his control over a regime characterized as Nigeria's most corrupt and brutal government. The execution of Ken Saro Wiwa, an Ogoniland political activist, inflamed ethnic tensions and sealed the Abacha government's fate as a pariah state.
The death of Abacha from a massive heart attack on 8 June 1998 paved the way for a democratic transition. Major General Abdulsalan Abubakar was selected as head of state in a closed-door meeting of the Provisional Ruling Council the following day. Abubakar honored his promise to restore democracy by releasing political prisoners, including Abiola and Obasanjo, in preparation for presidential elections. Obasanjo was elected president on 27 February 1999, and Abubakar stated, "I have no doubt democracy has come to stay."
Obasanjo was elected president by an unprecedented margin in the elections of April 2003 on his People's Democratic Party (PDP) ticket, but the results were widely rejected by the opposition parties who claimed they had been robbed of victory, and who under the banner of The Conference of Nigerian Political Parties, called for the formation of an Interim Government of National Unity headed by Nigeria's Chief Justice to conduct free, fair, and transparent elections. International observers also found the polls to be marred by manipulation and fraud, owing to a poor showing by INEC, Nigeria's electoral commission. In separate polls during April and early May, Obasanjo's PDP won an absolute majority in the national Parliament and governorships and legislative majorities in 28 of Nigeria's 36 states but the voting was marked by a light turn-out, as well as voter apathy.