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International law: from 1945 to date: Custom, GPs, Jus Cogens

Custom, General Principles, Jus Cogens, Peremptory Norms

International custom requires both state practice and proof of opinio juris sive necessitatis ie that the state had felt legally obliged to act in that way.

To find commentary on SOLO use subject search 

Customary law, International

Sources to establish a state's practice in international law

Try the official website of that government’s Ministry of Foreign Affairs or Ministry of External Affairs etc.

Many states publish an annuaire, Jahrbuck or yearbook on international law. (There is no unanimity with yearbook, year book or year-book).

Vienna Convention on the Law of Treaties (1969)
art. 53: A treaty is void if, at the time of its conclusion, it conflicts with a peremptory norm of general international law. For the purposes of the present Convention, a peremptory norm of general international law is a norm accepted and recognized by the international community of States as a whole as a norm from which no derogation is permitted and which can be modified only by a subsequent norm of general international law having the same character.
art. 66 (a) disputes on such a norm's existence can be submitted to ICJ.

Jus cogens (International law) is a specific subject search term to try in SOLO

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