Law of treaties

International Law · Treaties, diplomacy and responsibility. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.

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The idea

The Vienna Convention on the Law of Treaties 1969 defines a treaty as an international agreement concluded between states in written form and governed by international law, whatever its name. The central rule is pacta sunt servanda: every treaty in force binds its parties and must be performed in good faith.

A state gives consent by signature, ratification or accession. It may attach a reservation to limit the effect of some provisions for itself, if the treaty allows.

A treaty may be invalid, for example for coercion or conflict with jus cogens, a peremptory norm from which no derogation is permitted. It may also be ended for material breach or a fundamental change of circumstances.

Rules to remember

Article 26: pacta sunt servanda. Article 18: a signatory must not defeat the object and purpose before ratification.
Article 19: a reservation is not allowed if the treaty prohibits it or if it is incompatible with the treaty's object and purpose.
Article 24: a treaty enters into force as it provides, or when all negotiating states have consented to be bound.
A treaty creates neither duties nor rights for a third state without its consent.
Articles 53 and 64: a treaty conflicting with jus cogens is void; a new peremptory norm ends an existing conflicting treaty.
Article 52: a treaty procured by the threat or use of force contrary to the UN Charter is void.
Article 60: material breach allows termination or suspension. Article 62: rebus sic stantibus cannot be used against a boundary treaty.

Common mistake

Students treat rebus sic stantibus as an easy way out of a treaty. Article 62 is narrow: the change must be fundamental, unforeseen, and must radically transform obligations still to be performed; it never applies to boundary treaties.

Worked example

States A and B conclude a treaty fixing their land boundary along a river. Thirty years later A's economy collapses and A claims the treaty has ended because of a fundamental change of circumstances. Is the claim good?

Rebus sic stantibus is recognised in Article 62 of the Vienna Convention 1969, but only within strict limits.
Article 62 expressly says a fundamental change may not be invoked to end a treaty that establishes a boundary.
The treaty therefore stays in force and pacta sunt servanda applies.

Answer: No. A boundary treaty cannot be terminated on the ground of a fundamental change of circumstances.

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