The Nigerian Civil War (6 July 1967 15 January 1970; also known as the Nigerian-Biafran War or the Biafran War) was a civil war fought between the government of Nigeria and the Republic of Biafra, a secessionist state which had declared its independence from Nigeria in 1967. Nigeria was led by General Yakubu Gowon, while Biafra was led by Lt. Colonel Odumegwu Ojukwu. Biafra represented the nationalist aspirations of the Igbo ethnic group, whose leadership felt they could no longer coexist with the federal government dominated by the interests of the Muslim Hausa-Fulanis of northern Nigeria. The conflict resulted from political, economic, ethnic, cultural and religious tensions which preceded Britain's formal decolonization of Nigeria from 1960 to 1963. Immediate causes of the war in 1966 included ethno-religious violence and anti-Igbo pogroms in Northern Nigeria, a military coup, a counter-coup and persecution of Igbo living in Northern Nigeria. Control over the lucrative oil production in the Niger Delta also played a vital strategic role.Within a year, the Federal Government troops surrounded Biafra, captured coastal oil facilities and the city of Port Harcourt. A blockade was imposed as a deliberate policy during the ensuing stalemate which led to mass starvation. During the two and half years of the war, there were about 100,000 overall military casualties, while between 500,000 and 2 million Biafran civilians died of starvation.In mid-1968, images of malnourished and starving Biafran children saturated the mass media of Western countries. The plight of the starving Biafrans became a cause clbre in foreign countries, enabling a significant rise in the funding and prominence of international non-governmental organizations (NGOs). The United Kingdom and the Soviet Union were the main supporters of the Nigerian government, while France, Israel (after 1968) and some other countries supported Biafra. The United States' official position was one of neutrality, considering Nigeria as 'a responsibility of Britain', but some interpret the refusal to recognize Biafra as favouring the Nigerian government.

Biafra, officially the Republic of Biafra, was a secessionist state in West Africa that separated from Nigeria and existed from May 1967 to January 1970. Its territory consisted of the predominantly Igbo-populated former eastern region of Nigeria which is now divided into the present day southsouth and southeastern regions of Nigeria. Biafra was formed by Igbo nationalists in response to a series of ethnic tensions shortly after Nigerian independence in 1960 that culminated in the 1966 massacres of Igbo people and other southeastern ethnic groups living in northern Nigeria. The military of Nigeria proceeded to attack Biafra shortly after it declared independence in 1967, resulting in the start of the Nigerian Civil War (also known as the Nigerian-Biafran War).

Biafra was formally recognized by Gabon, Haiti, Ivory Coast, Tanzania, and Zambia. Other nations, which did not give official recognition but provided support and assistance to Biafra, included France, Spain, Portugal, Norway, Rhodesia, South Africa, and Vatican City. Biafra received aid from non-state actors, including Joint Church Aid, foreign mercenaries, Holy Ghost Fathers of Ireland, and under their direction Caritas International, and U.S. Catholic Relief Services. Médecins Sans Frontières also originated in response to the suffering.

After two-and-a-half years of war, during which almost two million Biafran civilians (three-quarters of them small children) died from starvation caused by the total blockade of the region by the Nigerian government, Biafran forces under Nigeria's motto of "No-victor, No-vanquished" surrendered to the Nigerian Federal Military Government (FMG). The surrender was facilitated by the Biafran Vice President and Chief of General Staff, Major General Philip Effiong, who assumed leadership of the Republic of Biafra after the original President, Colonel Chukwuemeka Odumegwu Ojukwu, fled to Ivory Coast. After the surrender of Biafra, some Igbos who had fled the conflict returned to their properties but were unable to claim them back from new occupants. This became law in the Abandoned Properties Act (28 September 1979). It was purported that at the start of the civil war, Igbos withdrew their funds from Nigerian banks and converted it to the Biafran currency. After the war, bank accounts owned by Biafrans were seized and a Nigerian panel resolved to give every Igbo person an account with only 20 pounds. Federal projects in Biafra were also greatly reduced compared to other parts of Nigeria. In an Intersociety study it was found that Nigerian security forces also extorted approximately $100 million per year from illegal roadblocks and other methods from Igboland – a cultural sub-region of Biafra in what is now southern Nigeria, causing greater mistrust of the Igbo citizenry towards the Nigerian security forces.