6 July 1967
Nigeria was created by the British without consideration of the country’s ethnic diversity. It has never truly integrated as one country. It served the British to have the country in turmoil because it would make it much easier for them to have access to the country’s rich oil resources. Nigeria has over 300 ethnic groups, with the more dominant being the Igbo in the East, the Hausa-Fulani in the North and the Yoruba in the West. When Nigeria gained independence from Britain, the three major ethnic groups in the west, South and North of the country, and which always had their own administration, culture and religious beliefs, were now forced into a unitary state. This proved to be an impossible task. The Westerners (mostly Yorubas) broke away from Nigeria declaring themselves the state of Biafra. This did not sit well with the easterners who saw the break away as illegal since they were not consulted. On 6 July 1967, a war broke out when the easterners tried to force the west to integrate back into Nigeria.
References

Atofarati A A. The Nigerian Civil War, Causes, Strategies, and Lessons Learnt from Africa Master Web [online] Available at: www.africamasterweb.com [Accessed on 25 June 2012]|Phillips B.  Biafra: Thirty years on from BBC News [online] Available at: www.news.bbc.co.uk [Accessed on 25 June 2012]