In January 1966 the civil government of Nigeria was overthrown by army officers belonging to the Igbo ethnic group and replaced by a military government under Major General Aguiyi-Ironsi. In July a second coup by Hausa officers of the Northern Region removed the government, prompting the murder of Igbos in the north and the mass migration of their numbers to Nigeria's Eastern Region. Following the failure of negotations, Lt. Col. Chukuemeka Odumegwu Ojukwu proclaimed the secession of the Eastern Region on 30 May 1967 and its establishment as the Republic of Biafra. In response, the federal government declared war and imposed economic sanctions. After initial successes in the war the Biafran army suffered heavy losses and severe food shortages. In October 1967 the capitial Enugu fell to Nigerian forces. Ojukwu fled the country on 11 January 1970, and Biafra formally surrendered on 15 January.