In 1970, after nearly three years of fighting, Biafran soldiers who were outnumbered 10 to one by federal troops and under-equipped, laid down their arms.
The conflict caused an estimated million deaths, many of them caused by starvation after the secessionist region was blockaded.
With surrender went their dreams of a separate state for the Igbo people, who are the majority in the southeast.
50 years after the fact, Biafra remains an extremely sensitive subject in Nigeria.
The sentiments among the Igbos is that they have totally been marginalised and excluded from the commanding heights of the Nigerian State.
“Nigeria did nothing for us since the end of the war. We have no roads, no infrastructures, no jobs. It’s time to achieve what our fathers started,” John Ahaneku, 48, told AFP.
Pro Biafran supporters in Aba
A study this month by London-based SBM Intelligence suggested there was “rising support for a Biafra” in Nigeria’s southeast and south.
“A total of 42.5 percent of all respondents believe that both regions should make up a future Biafran state,” it said.
“However, just under half, 49.3 percent, of the total respondents still believe that the way forward for the Nigerian state is as one country, but with ‘true federalism’ being practiced.”
Igbo frustrations have grown over the decades.
During the long years of military government after the end of the war, they felt excluded from economic and political power.
Both have been dominated by the two other main ethnic groups in the country, the northern Hausa-Fulani and the Yoruba from the southwest.
But it was only after the return to democracy in 1999 that secessionist aspirations began to slowly resurface.
The current main pro-independence groups want a referendum on self-determination.
They accuse the former military ruler Muhammadu Buhari — a northern Muslim who was elected civilian president in 2015 — of violently repressing their freedom of expression.
The arrest and incarceration towards the end of 2015 of IPOB leader Nnamdi Kanu on treason charges have been seen as a turning point.
As Nigeria marks 50 years since the declaration of an independent state of Biafra, the main pro-independence groups — the Indigenous People of Biafra (IPOB), and the Movement for the Actualisation of the Sovereign State of Biafra (MASSOB) — have called for a day of reflection.
People in the southeast have been urged to stay at home to commemorate the secession, which happened on May 30, 1967.
But many fear an eruption of violence and Nigeria’s security forces have said they are on red alert in hotspots in the former republic, such as Aba and Onitsha, where protests last year turned bloody.
Additional report from AFP