Nigerian Civil War, the claims of fraud led to a military coup on January 15, 1966 by left-leaning junior Army officers mostly majors and captains. This coup led to the accession of General Johnson Aguiyi-Ironsi , the head of the Nigerian Army, as head of state of Nigeria. This coup benefited mostly the Igbos because most of the coup plotters were Igbos and Ironsi, an Igbo, promoted many Igbos in the Army at the expense of Yoruba and Hausa officers. On the 29th of July 1966, the Northerners executed a counter-coup. This coup was led by Lt. Col. Murtala Muhammed. It placed Lt. Col. Yakubu Gowon into power. Ethnic tensions due to the coup and counter-coup increased and led to the large-scale massacres of Christian Igbos living in the Muslim north.