Law and Practice as to Treaties — Public International Law Notes

Law and Practice as to Treaties

In 1969, after almost twenty years of work, the international community produced the “treaty on treaties” — the Vienna Convention on the Law of Treaties. It is the single most important instrument in this whole subject, because treaties are how States make almost all their law. If you can explain how a treaty is born (formation), why it binds (pacta sunt servanda), and how it ends (termination), you have the topic.

Treaties — formation, binding force, interpretation, termination

A treaty is an international agreement concluded between States in written form and governed by international law (VCLT Art. 2). It goes by many names — convention, pact, protocol, charter, covenant — but the substance is the same. The whole law is in the Vienna Convention on the Law of Treaties (VCLT, 1969), in four blocks.

A. Definition and classification

Law-making treaties — lay down general rules for many States (the UN Charter, the Geneva Conventions).
Treaty-contracts — settle a specific matter between two or a few States (a boundary treaty, a trade deal).
Bilateral (two parties) and multilateral (many parties).

Learn the stages in order:

Accrediting of representatives — negotiators act under full powers (a document authorising them to bind the State).
Negotiation and adoption of the text.
Signature — authenticates the text; it may or may not bind, depending on whether ratification is needed.
Ratification — the formal confirmation by the State’s competent authority; where required, the treaty binds only on ratification, not on mere signature.
Accession — a State that did not sign joining an existing treaty.
Reservations — a State may exclude/modify the effect of certain provisions, if not prohibited and not incompatible with the treaty’s object and purpose.
Registration (Art. 102, UN Charter) — treaties are to be registered with the UN Secretariat; an unregistered treaty cannot be invoked before UN organs.
Entry into force — as the treaty provides.

C. Binding force and interpretation

Pacta sunt servanda (Art. 26) — “every treaty in force is binding upon the parties and must be performed in good faith”. This is the cornerstone.
A treaty binds only the parties (pacta tertiis nec nocent nec prosunt — it neither harms nor benefits third States without their consent).
Interpretation (Art. 31) — a treaty is interpreted in good faith, according to the ordinary meaning of its terms in their context and in the light of its object and purpose.

D. Vitiating factors (grounds of invalidity)

Consent may be vitiated by: error (Art. 48), fraud (Art. 49), corruption of a representative (Art. 50), coercion of the representative (Art. 51 — voids consent absolutely), coercion of the State by force (Art. 52), and conflict with a peremptory norm / jus cogens (Art. 53 — void from the start).

E. Termination

A treaty may end by: performance or expiry of its term; agreement of the parties; material breach by one party entitling the other to terminate (Art. 60); supervening impossibility of performance (Art. 61); a fundamental change of circumstances — rebus sic stantibus [things thus standing] (Art. 62); outbreak of war between the parties; and the emergence of a new jus cogens norm with which the treaty conflicts (Art. 64).

Article 26, VCLT (1969): “Every treaty in force is binding upon the parties to it and must be performed by them in good faith.” (Pacta sunt servanda.)

Article 62, VCLT (1969): a fundamental change of circumstances not foreseen by the parties may be invoked to terminate a treaty only where those circumstances were an essential basis of consent and the change radically transforms the obligations still to be performed (rebus sic stantibus).

In Simple Terms: A treaty is a written deal between States. It is made in stages — negotiate, sign, and (where needed) ratify — and once in force it must be kept in good faith (pacta sunt servanda, Art. 26). It can be attacked if consent was got by error, fraud or coercion, and it ends by expiry, agreement, serious breach, impossibility, a fundamental change of circumstances (rebus sic stantibus, Art. 62), or war.

🧩 WORKED EXAMPLE — coercing the representative (Art. 51)

Facts. State A obtains State B’s consent to a treaty by coercing B’s representative with personal threats. A now wants to enforce the treaty.

Rule. Coercion of a State’s representative through acts or threats directed against him voids consent absolutely (Art. 51 VCLT, 1969).

Apply. The decoy is that B’s representative did in fact sign, so consent “looks real”. But consent extracted by personal coercion of the representative is a nullity under Art. 51 — it is void, not merely voidable, and cannot be cured or ratified.

Conclusion. The treaty is void for want of valid consent; A cannot enforce it. (Note the parallel: coercion of the State itself by force voids the treaty under Art. 52.)

flowchart TD
    A["Treaty (VCLT 1969)"]
    A --> B["Formation: full powers -> negotiation -><br/>signature -> ratification -> accession -><br/>registration (Art. 102) -> in force"]
    A --> C["Binding: pacta sunt servanda (Art. 26)"]
    A --> D["Invalidity: error, fraud, corruption,<br/>coercion (Arts. 51-52), jus cogens (Art. 53)"]
    A --> E["Termination: expiry, agreement, breach (Art. 60),<br/>impossibility (Art. 61), rebus sic stantibus (Art. 62), war"]
    classDef box fill:#e8f0fe,stroke:#333,color:#111;
    class A,B,C,D,E box;

Case Laws

Gabcikovo-Nagymaros Project (Hungary v. Slovakia, 1997, ICJ) — rebus sic stantibus and impossibility are narrowly confined; pacta sunt servanda prevails unless the strict conditions of Arts. 61–62 are met.
Fisheries Jurisdiction Case (UK v. Iceland, 1973, ICJ) — a fundamental change of circumstances (Art. 62) may be invoked only where the changed circumstances were an essential basis of consent and radically transform the obligation.

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Law and Practice as to Treaties — Public International Law Notes