Successor State

In international law, state succession occurs when one state replaces another in the responsibility for the international relations of a territory. The replacing entity is the successor state; the prior entity is the predecessor state. Succession can follow decolonization, dissolution, secession, unification, or merger, and it raises questions about which treaties, debts, assets, archives, and memberships transfer to the new sovereign.

Two principal treaties codify the rules, though both have limited ratification:

• The Vienna Convention on Succession of States in Respect of Treaties (1978), which entered into force in 1996.
• The Vienna Convention on Succession of States in Respect of State Property, Archives and Debts (1983), which has not entered into force.

Customary international law and case-by-case practice therefore remain decisive. A common distinction is between continuator states, which retain the predecessor's legal personality and UN seat, and successor states, which must apply afresh. After the dissolution of the USSR in 1991, the Russian Federation was accepted as the continuator, taking the Soviet permanent seat on the UN Security Council, while the other former Soviet republics joined the UN as new members. By contrast, the Socialist Federal Republic of Yugoslavia was deemed to have dissolved; the Badinter Arbitration Committee (1991–1992) concluded that all five emerging republics were successor states on an equal footing, and the Federal Republic of Yugoslavia was eventually required to apply for UN membership in 2000.

Other illustrative practice includes the Czech Republic and Slovakia (1993), which jointly succeeded Czechoslovakia and split assets and debts roughly 2:1 by population; South Sudan (2011), which seceded from Sudan and negotiated oil revenues and external debt separately; and Germany (1990), where reunification was treated as the absorption of the GDR by the FRG rather than the creation of a new state.

Key issues typically negotiated include treaty continuity, sovereign debt apportionment, nationality of inhabitants, diplomatic property, and membership in international organizations.