International Law Beginner's Guide
Treaties, custom, jus cogens — the sources of law that bind states across borders.
Sources
ICJ Statute Article 38
The most authoritative listing of international law sources.
Key Points
- International conventions (treaties).
- International custom (state practice + opinio juris).
- General principles of law recognized by civilized nations.
- Judicial decisions and scholarly writings (subsidiary means).
Treaties
Written agreements between states, governed by the Vienna Convention on the Law of Treaties (VCLT 1969).
Negotiation + adoption
Delegates negotiate; text adopted (often by consensus).
Signature
Authenticates text and expresses political commitment; doesn't yet bind.
Ratification
Domestic process (US: Senate 2/3; UK: crown prerogative + Parliament notice). Binds the state once complete.
Entry into force
Usually after a minimum number of ratifications (Rome Statute needed 60; entered force July 1, 2002).
Reservations
Unilateral statements modifying treaty effect for that state. Must not defeat the object and purpose (VCLT Art 19).
Customary international law
Practice that states follow out of a sense of legal obligation. Two elements: state practice + opinio juris.
Key Points
- State practice: consistent, general, representative behavior.
- Opinio juris: states believe the practice is legally required.
- Persistent objector rule: a state that consistently objects from the outset can avoid being bound.
- Examples: prohibition on torture, diplomatic immunity, freedom of navigation.
Jus cogens
Peremptory norms from which no derogation is permitted — even by treaty. The highest tier of international law.
Key Points
- Accepted jus cogens: genocide, slavery, torture, aggression, apartheid.
- Treaties conflicting with jus cogens are void (VCLT Art 53).
- International Law Commission's 2022 draft conclusions formalized existing practice.
Structure
Subjects of international law
Key Points
- States: primary subjects — sovereign equality (UN Charter Art 2(1)).
- International organizations: derived legal personality (Reparations Advisory Opinion, 1949).
- Individuals: limited but growing — international criminal law, human rights.
- Non-state actors: armed groups, corporations — treated ad hoc.
Monism vs dualism
How domestic legal systems treat international law.
Monism
International and domestic law are one system. International law directly applies. Netherlands, France.
Dualism
Separate systems. International law applies domestically only via domestic implementing legislation. UK, most Commonwealth countries.
Hybrid (US)
Self-executing vs non-self-executing treaties; Foster v. Neilson (1829) is the foundation. Most US treaties require implementing legislation.
Applying the Law
Treaty interpretation
VCLT Articles 31-33 govern. Text → context → object and purpose. Supplementary means only if the ordinary rule produces ambiguous or absurd results.
State responsibility
When states breach obligations, consequences follow. ILC's 2001 Articles on State Responsibility are the authoritative source.
Key Points
- Attribution: the act must be attributable to the state.
- Breach: international obligation must be violated.
- Consequences: cessation, reparation, non-repetition.
- Defenses: necessity, force majeure, self-defense, consent, countermeasures.
FAQ
Why do states comply with international law?
Chayes & Chayes (1995): the managerial model — compliance is largely about capacity, not intent. Keohane: reputation, reciprocity, institutions. Most compliance is quiet and routine; high-profile violations are the exception.
How is international law enforced?
Diffusely. ICJ decisions are binding but unenforceable without Security Council support. Trade retaliation (WTO), sanctions (UNSC), domestic courts applying international norms. Enforcement is weakest where it matters most.
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