Between 1960 and 1980 Nigeria experienced all the following system of government except

Between 1960 and 1980, Nigeria experienced all the listed systems of government except confederalism. Confederalism is a system of government in which several states or regional governments come together to form a loose union with a weak central government that has limited power. During this period, Nigeria started out as a federal system of government at independence in 1960, and continued as such until the civil war in 1967, when it briefly became a unitary system. After the civil war, Nigeria returned to a federal system in 1970, and remained so until the military coup of 1983, which ushered in a presidential system of government. Therefore, the correct answer is "confederal."