Succession of states refers to the situation when one state replaces another in the responsibility for the international relations of a territory.  This can occur, for example, when a colonial power relinquishes its control over a territory — as happened in most of Africa on gaining independence from European states from the late 1950s.  Alternatively it may happen when a part of a state breaks away to form a new state, as in the case of Eritrea and South Sudan. State succession also occurs when sovereignty over a territory is transferred from one territory to another, as has happened to the Bakassi Peninsula between Nigeria and Cameroon.

State succession raises particular issues for citizenship.  The default rule in international law is that a person should, in the absence of other agreement, acquire or retain a nationality based on habitual residence.  Every person who was the national of a predecessor state should have the nationality of at least one successor state. But there are many cases where these rules protecting against statelessness have not been respected.

The International Law Commission has adopted important Articles on the Nationality of Natural Persons in relation to the Succession of States that are the leading guidance for states on nationality in the context of state succession.