Succession of states is a theory and practice in international relations regarding the recognition and acceptance of a newly created sovereign state by other states, based on a perceived historical relationship the new state has with a prior state. The theory has its root in 20th century diplomacy.
Succession may refer to the transfer of rights, obligations, and/or property from a previously well-established prior state (the predecessor state) to the new one (the successor state). Transfer of rights, obligations, and property can include overseas assets (embassies, monetary reserves, museum artifacts), participation in treaties, membership in international organizations, and debts. Often a state chooses piecemeal whether or not it wants to be considered the successor state. A special case arises, however, when the predecessor state was signatory to a human rights treaty, since it would be desirable to hold the successor state accountable to the terms of that treaty, regardless of the successor state's desires.
A difficulty arises at the dissolution of a larger territory into a number of independent states. What may become a matter of contention is a situation where one successor state seeks either to continue to be recognised under the same federal name of that of its predecessor or to assume the privileged position in international organisations held by the preceding federation. Such states are then considered as a "continuator state".
International convention since the end of the Cold War has come to distinguish two distinct circumstances where such privileges are sought by such a successor state, in only the first of which may such successor states assume the name or privileged international position of their predecessor. The first set of circumstances arose at the dissolution of the Union of Soviet Socialist Republics (USSR) in 1991. One of this federation's constituent republics, the Russian Federation, was declared the USSR's continuator state on the grounds that it contained 51% of the population of the USSR and 77% of its territory. In consequence, Russia agreed that it would acquire the USSR's seat as a permanent member of the United Nations Security Council. This was also accepted by the rest of the former states of the USSR; in a letter dated 24 December 1991, Boris Yeltsin, at the time President of the Russian Federation, informed the Secretary-General that the membership of the Soviet Union in the Security Council and all other United Nations organs was being continued by the Russian Federation with the support of the 11 member countries of the Commonwealth of Independent States. All Soviet embassies became Russian embassies.
On the other hand, the Baltic states represent a special case. Due to the non-recognition by the majority of states of the incorporation of Estonia, Latvia and Lithuania into the Soviet Union in 1940, most states accepted the claim by the Baltic states that they had restored their independence in 1991 and were identical to the pre-1940 states, and thus were not considered to be successor states of the Soviet Union. As a consequence, the Baltic states were able to simply re-establish diplomatic relations with many countries, re-affirm pre-1940 treaties still in force and resume membership to many international organisations.
There are several recent examples where succession of states, as described above, has not been entirely adhered to. This is only a list of the exceptions that have occurred since the creation of the United Nations. In previous historical periods, the exceptions would be too many to list.
Bühler, Konrad G. (2001). State Succession and Membership in International Organizations. Legal Aspects of International Organization Series. Volume 38. Martinus Nijhoff Publishers. p. 161-4. ISBN 9789041115539.
"Member States of the United Nations - Russia*". the United Nations. Retrieved 28 December 2013.
Bühler, Konrad G. (2001). State Succession and Membership in International Organizations. Legal Aspects of International Organization Series. Volume 38. Martinus Nijhoff Publishers. p. 177-9. ISBN 9789041115539.
Burgenthal/Doehring/Kokott: Grundzüge des Völkerrechts, 2. Auflage, Heidelberg 2000 (German)
European Journal of International Law – State Succession in Respect of Human Rights Treaties
Wilfried Fiedler: Der Zeitfaktor im Recht der Staatensukzession, in: Staat und Recht. Festschrift für Günther Winkler, Wien, 1997, S. 217-236. (German)
Wilfried Fiedler: Staatensukzession und Menschenrechte, in: B. Ziemske u.a. (Hrsg.), Festschrift für Martin Kriele, München 1997, S. 1371-1391 (German)