Concept:Military intervention means the armed forces taking over the government from civilian rulers.Explanation:The first military intervention in Nigeria occurred in the year 1966. Young army officers led a coup that removed the civilian government of Prime Minister Alhaji Tafawa Balewa. General Aguiyi Ironsi later assumed power as the military Head of State. He suspended the constitution and introduced a unitary system of government. The military claimed the intervention was to stop corruption and reduce ethnic tension.Answer:B. 1966