When the civil war in Nigeria ended in January 1970 I was frequently confronted with problems concerning the legality of acts done during the secession by the secessionist regime and by individuals - contracts entered into, property seized or destroyed, appointments made or terminated, currency issued, and sentences or judgments passed by the regular courts and the special tribunals. This raises the whole question of the constitutionality of the secession and of the secessionist regime. If the regime was unconstitutional, could anything done under it have legal effect? Secession in Nigeria was of course preceded, if not caused, by the events of January 1966 when the civilian government handed over power to the military. That event was unique, for never before has a civilian government voluntarily abdicated in favour of the military. But what in fact was the true constitutional significance of that event ? Was it a coup d’etat or a normal change of government under the Constitution, and what is the nature of the military government established as a result? When I began probing these questions, I found myself confronted by other examples of constitutional breakdown in certain emergency situations.