Several dominant themes in Nigerian history are essential for understanding contemporary Nigerian politics and society. First, the spread of Islam, predominantly in the north but later in southwestern Nigeria as well, began a millennium ago. The creation of the Sokoto Caliphate in the jihad (holy war) of 1804–8 brought most of the northern region and adjacent parts of Niger and Cameroon under a single Islamic government. The great extension of Islam within the area of present-day Nigeria dates from the nineteenth century and the consolidation of the caliphate. This history helps account for the dichotomy between north and south and the divisions within the north that have been so pronounced during the colonial and postcolonial eras. Second, the slave trade across both the Sahara Desert and the Atlantic Ocean had a profound influence on virtually all parts of Nigeria. The transatlantic trade in particular accounted for the forced migration of perhaps 3.5 million people between the 1650s and the 1860s, while a steady stream of slaves flowed north across the Sahara for a millennium, ending only at the beginning of the twentieth century. Within Nigeria slavery was widespread and bore social implications that are still evident. Conversion to Islam and the spread of Christianity were intricately associated with issues relating to slavery and with efforts to promote political and cultural autonomy. Third, the colonial era was relatively brief, lasting only six decades or so depending on the part of Nigeria, but it unleashed such rapid change that the full impact is still felt in the contemporary period.

Early History: All evidence suggests the early settlement of Nigeria millennia before the spread of agriculture 3,000 years ago. The earliest culture in Nigeria is identifiable by the distinctive artifacts of the Nok people. These skilled artisans and ironworkers flourished between the fourth century B.C. and the second century A.D. in a large area above the confluence of the Niger and Benue rivers. The Nok achieved a level of material development not repeated in the region for nearly 1,000 years.

Long before 1500, much of present-day Nigeria was divided into states, which can still be linked to the modern ethnic groups that trace their history to the origins of these states. These early states included the Yoruba kingdoms, the Edo kingdom of Benin, the Hausa cities, and Nupe. In addition, numerous small states to the west and south of Lake Chad were absorbed or displaced in the course of the expansion of Kanem, centered to the northeast of Lake Chad. Borno, initially the western province of Kanem, became independent in the late fourteenth century.

The sixteenth century marked a high point in the political history of northern Nigeria. During this period, the Songhai Empire reached its greatest limits, stretching from the Senegal and Gambia rivers in the far west and incorporating part of Hausaland in the east. At the same time, the Sayfawa Dynasty of Borno asserted itself, conquering Kanem and extending its control westward to Hausa cities that were not under Songhai imperial rule. For almost a century, much of northern Nigeria was part of one or the other of these empires, and after the 1590s, Borno dominated the region for 200 years. Despite Borno’s hegemony, the Hausa states wrestled for ascendancy among themselves for much of the seventeenth and eighteenth centuries.

European Slave Trade in West Africa: By 1471 Portuguese ships had reconnoitered the West African coast south as far as the Niger Delta. Portugal's lasting legacy for Nigeria was its initiation of the transatlantic slave trade. The Portuguese monopoly on West African trade was broken at the end of the sixteenth century when Portugal's influence was challenged by the rising naval power of the Netherlands. The Dutch took over Portuguese trading stations on the coast that were the source of slaves for the Americas. French and British competition later undermined the Dutch position, and Britain became the dominant slaving power in the eighteenth century.

By the end of the eighteenth century, the area that was to become Nigeria was far from a unified country. Furthermore, the orientation of the north and the south was entirely different. The savanna states of Hausaland and Borno in the north had experienced a difficult century of political insecurity and ecological disaster but otherwise continued in a centuries-long tradition of slow political and economic change that was similar to other parts of the savanna. The southern areas near the coast, by contrast, had been swept up in the transatlantic slave trade. Political and economic change had been rapid and dramatic. By 1800 Oyo, a constitutional monarchy, governed much of southwestern Nigeria, while the Aro, another polity, had consolidated southeastern Nigeria into a confederation. Both Oyo and the Aro confederacy were major trading partners of the slave traders from Europe and North America.

In the first decade of the nineteenth century, two unrelated developments that were to have a major influence on virtually all of the area that is now Nigeria ushered in a period of radical change. First, between 1804 and 1808 the Islamic holy war of Usman dan Fodio established the Sokoto Caliphate, a loose confederation of emirates centered in northwestern Nigeria. By the middle of the nineteenth century, when the Sokoto Caliphate was at is greatest extent, it comprised 30 emirates and the capital district of Sokoto. All the important Hausa emirates, including Kano, the wealthiest and most populous, were directly under Sokoto. Second, in 1807 Britain declared the transatlantic slave trade to be illegal, an action that occurred at a time when Britain itself was responsible for shipping more slaves to the Americas than any other country. Although the transatlantic slave trade did not end until the 1860s, other commodities, especially palm oil, gradually replaced it. The shift in trade had serious economic and political consequences in the interior, which led to increasing British intervention in the affairs of Yorubaland and the Niger Delta.

Colonial Nigeria: In 1885 at the Berlin Conference, the European powers attempted to resolve their conflicts of interest in Africa by allotting areas of exploitation. The conferees also enunciated the principle, known as the “dual mandate,” that the interests of both Europe and Africa would best be served by maintaining free access to the African continent for trade and by providing Africa with the benefits of Europe's civilizing mission. Britain's claims to a sphere of influence in the Niger Basin were acknowledged formally, but it was stipulated that only effective occupation would secure full international recognition. In the end, pressure from France and Germany hastened the establishment of effective British occupation and the creation of protectorates in northern and southern Nigeria.

Frederick Lugard, who assumed the position of high commissioner of the Protectorate of Northern Nigeria in 1900, was occupied with transforming the commercial sphere of influence inherited from the Royal Niger Company into a viable territorial unit under effective British political control. His objective was to conquer the entire region and to obtain recognition of the British protectorate by its indigenous rulers, especially the Fulani emirs of the Sokoto Caliphate. Lugard's campaign systematically subdued local resistance, using armed force when diplomatic measures failed. Lugard's success in northern Nigeria has been attributed to his policy of indirect rule, which called for governing the protectorate through the rulers who had been defeated. If the emirs accepted British authority, abandoned the slave trade, and cooperated with British officials in modernizing their administrations, the colonial power was willing to confirm them in office. Lugard's immediate successor, Hugh Clifford (1919–25), introduced a diametrically opposed approach emphasizing Western values. In contrast to Lugard, Clifford restricted the power of the northern emirs by scaling back indirect rule, while in the south he saw the possibility of building an elite educated in European-style schools.

British colonialism created Nigeria, joining diverse peoples and regions in an artificial political entity with little sense of a common Nigerian nationality. Inconsistencies in British policy reinforced cleavages based on regional animosities by attempting simultaneously to preserve the indigenous cultures of each area and to introduce modern technology and Western political and social concepts. In the north, appeals to Islamic legitimacy upheld the rule of the emirs, so that nationalist sentiments there were decidedly anti-Western. Modern nationalists in the south, whose thinking was shaped by European ideas, opposed indirect rule, which had entrenched what was considered to be an anachronistic ruling class in power and shut out the Westernized Nigerian elite.

Independence and Civil War: By an act of the British Parliament, Nigeria became an independent country within the Commonwealth on October 1, 1960. In 1963 Nigeria became a republic within the Commonwealth. The change in status called for no practical alteration of the constitutional system. The president, elected to a five-year term by a joint session of the parliament, replaced the crown as the symbol of national sovereignty and the British monarchy as head of state. Nnamdi Azikiwe became the republic's first president.

Although the first postindependence parliamentary elections were held in December 1964, the nation’s leadership in the several decades following independence was determined by coup, not by election, and by military, rather than civilian government. One of the most important developments during the 1960s was the declaration of independence by the Eastern Region in 1967, followed by a 30-month civil war. In the face of increased sectarian violence, the Eastern Region's military governor, Lieutenant Colonel Chukwuemeka Odumegwu Ojukwu, was under pressure from Igbo (also seen as Ibo) officers to assert greater independence from the Federal Military Government (FMG). Ultimately, on May 30, 1967, Ojukwu proclaimed the independent Republic of Biafra, named after the Bight of Biafra. He cited as the principal cause for this action the government's inability to protect the lives of predominantly Igbo easterners and suggested its culpability in genocide.

Initially, the FMG launched "police measures" to restore the authority of Lagos in the Eastern Region, but soon full-scale civil war broke out. Finally, in January 1970 Biafran resistance collapsed, and the FMG reasserted its authority over the area. An estimated 1 to 3 million died from hostilities, disease, and starvation during the civil war, and more than 3 million Igbo became refugees. The economy of the region was shattered. In several years, however, the state government achieved the rehabilitation of 70 percent of the industry incapacitated during the war. The federal government granted funds to cover the state's operating expenses for an interim period, and much of the war damage was repaired.

Coups and Mostly Military Government: In the postwar period, all significant political power remained concentrated in the FMG. The influence of Yakubu (Jack) Gowon, who had come to power in a 1966 coup, depended on his position as chairman of the Supreme Military Council, which was created in March 1967. The regime ruled by decree. In October 1970, Gowon announced his intention of staying in power until 1976, the target year for completion of the military’s political program and return to an elected civilian government. But many Nigerians feared that the military planned to retain power indefinitely. In 1972 Gowon partially lifted the ban on political activity that had been in force since 1966 in order to permit a discussion of a new constitution that would pave the way for civilian rule. The debate that followed was ideologically charged, and Gowon abruptly terminated the discussion.

The Gowon regime came under fire because of widespread and obvious corruption at every level of national life. Inefficiencies compounded the effect of corruption. Crime also posed a threat to national security and had a seriously negative impact on efforts to bring about economic development. The political atmosphere deteriorated to the point where Gowon was deposed in a bloodless military coup in July 1975. The armed forces chose as Gowon’s successor Brigadier (later General) Murtala Ramat Muhammad, a Muslim northerner. Muhammad was assassinated during an unsuccessful coup in February 1976, but in a short time his policies had won him broad popular support, and his decisiveness elevated him to the status of national hero. He had sought to restore public confidence in the federal government, reduce government expenditures on public works, and encourage the expansion of the private sector. He also set in motion the stalled machinery of devolution to civilian rule by a commitment to hand over power to a democratically elected government by October 1979.

Lieutenant General Olusegun Obasanjo, a Yoruba, succeeded Muhammad. Keeping the established chain of command in place, Obasanjo pledged to continue the program for the restoration of civilian government in 1979 and to carry forward the reform program to improve the quality of public service. In 1979 under Obasanjo’s leadership, Nigeria adopted a constitution based on the Constitution of the United States that provided for a separation of powers among the executive, legislative, and judicial branches. The country was now ready for local elections, to be followed by national elections that would return Nigeria to civilian rule. Obasanjo also initiated plans to move the federal capital from Lagos to a more central location in the interior at Abuja. Ultimately, Abuja became the country’s capital in December 1991.

The Second Republic, 1979–83: In 1979 five revamped parties competed in national elections, marking the beginning of the Second Republic. The presidential succession from Obasanjo to a civilian, President Alhaji Shehu Shagari, was the first peaceful transfer of power since independence. Nigeria’s Second Republic was born amid great expectations. Oil prices were high, and revenues were on the increase. It appeared that unlimited development was possible. Unfortunately, the euphoria was short-lived. A number of weaknesses beset the Second Republic. First, the coalition that dominated federal politics was not strong, and in effect the victorious National Party of Nigeria (NPN) led by Shagari governed as a minority. Second, there was a lack of cooperation between the NPN-dominated federal government and the 12 states controlled by opposition parties. Third, and perhaps most importantly, the oil boom ended in mid-1981, precisely when expectations of continuous growth and prosperity were at a height. The recession that set in put severe strains on the Second Republic.

Return to Military Rule: On December 31, 1983, the military seized power once again, primarily because there was virtually no confidence in the civilian regime. Allegations of fraud associated with Shagari’s re-election in 1983 served as a pretext for the takeover, although the military was in fact closely associated with the ousted government. Ominously, the economy was in chaos. The true cost of the failure to use earlier revenues and foreign reserves to good effect now became apparent. The leader of the coup d'état was Major General Muhammadu Buhari, a Hausa whose background and political loyalties tied him closely to the Muslim north and the deposed government. The military regime tried to achieve two goals. First, it attempted to secure public support by reducing the level of corruption; second, it demonstrated its commitment to austerity by trimming the federal budget. In a further effort to mobilize the country, Buhari launched a “War Against Indiscipline” in the spring of 1984. This national campaign, which lasted 15 months, preached the work ethic, emphasized patriotism, decried corruption, and promoted environmental sanitation. However, the campaign achieved few of its aims.

The economic crisis, the campaign against corruption, and civilian criticism of the military undermined Buhari's position, and in August 1985 a group of officers under Major General Ibrahim Babangida removed Buhari from power. The Babangida regime had a rocky start. A countercoup in December 1985 failed but made it clear that not everyone in the military sided with the Armed Forces Ruling Council, which succeeded the Supreme Military Council. The most serious opposition centered in the labor movement and on university campuses. There was also considerable controversy over Nigeria's entry into the Organization of the Islamic Conference, an international body of Muslim states, in 1986. Buhari's regime had initiated the application, which Babangida allowed to stand. The strong reaction among many Christians proved to be an embarrassment to the regime.

Babangida addressed the worsening recession through the structural adjustment program of 1986. However, despite US$4.2 billion of support from the World Bank and the rescheduling of foreign debt, the recession led to a series of currency devaluations, a decline in real income, and rising unemployment during the second half of the 1980s. Babangida remained in power until 1993, when he ushered in an Interim National Government under the leadership of Chief Ernest Shonekan. This step followed the military’s annulment of election results in June 1993.

In November 1993, General Sani Abacha seized control from the caretaker government and served as military dictator until his death in 1998. During his rule, Abacha suppressed dissent and failed to follow through with a promised transition to civilian government. In 1995, as a result of various human rights violations, the European Union, which already had imposed sanctions in 1993, suspended development aid, and Nigeria was temporarily expelled from the Commonwealth. Corruption also flourished, and Abacha was later found to have siphoned off oil revenues into personal bank accounts in Switzerland. In 2005 Nigeria began to recover US$458 million of illicit funds deposited in Swiss banks during the Abacha regime.

Transition to Civilian Government: Upon Abacha’s death in June 1998, his chief of defense staff, Major General Abdulsalami Abubakar, assumed control and began to release political prisoners, including the former leader Obasanjo. Local government elections were held in December 1998, state legislative elections followed in January 1999, and federal legislative and presidential elections completed the transition to civilian government in February 1999. Obasanjo was elected president, and his party, the People’s Democratic Party, won a majority of the seats in both the Senate and House of Representatives, amidst ever-present allegations of election irregularities. Fifteen years of military rule had come to an end, and Nigeria entered the longest period of civilian rule since independence. In 2003 Obasanjo and his party won re-election, and speculation mounted that the Nigerian leader might seek a constitutional change that would permit him to run for a third term in 2007. (In May 2006, the Nigerian Senate rejected a constitutional amendment that would have permitted a third term.)

Obasanjo succeeded in establishing civilian rule based on a multiparty democracy and launched a campaign against corruption, but despite a surge in oil revenues that buoyed the federal coffers, his administration faced a number of serious challenges. In 2000 religious tensions spiked following the imposition of sharia, or Islamic law, in 12 northern, predominantly Muslim states. These tensions hindered cooperation between the president and the National Assembly, among the states, and between the states and the federal government. In 2004 religious strife forced the government to declare a state of emergency in centrally located Plateau State. Ethnic strife further complicated matters, notably in the southeastern state of Benue, where tribal warfare broke out in 2001, and in the oil-rich Niger Delta, where the Ijaw tribe continues to conduct an insurgency against international energy facilities and workers. Nigeria’s image of playing a constructive role in regional stability was tarnished in 2002 when the International Criminal Court granted Cameroon control over the disputed Bakasi Peninsula, but Nigeria refused to comply with the ruling.