International Law, Treaties and Diplomatic Practice
Sources and structure
Article 38 of the ICJ Statute lists sources: treaties, custom, general principles, judicial decisions and teachings as subsidiary means. Custom requires state practice plus opinio juris; persistent objectors are exempt. Distinguish jus cogens (peremptory norms: genocide, slavery, aggression) and erga omnes obligations. Know the Vienna Convention on the Law of Treaties (1969): signature versus ratification, reservations, pacta sunt servanda, rebus sic stantibus, and jus cogens voiding treaties.
Jurisdiction and responsibility
Territoriality, nationality, protective and universal jurisdiction (piracy, genocide, war crimes). State responsibility requires attribution plus breach, with defences of consent, necessity and countermeasures. Immunity: sovereign immunity and diplomatic immunity under the Vienna Convention on Diplomatic Relations (1961) - inviolability of mission and agents, persona non grata, and the distinction between diplomatic and consular functions (1963 Convention).
Law of the sea and use of force
UNCLOS (1982): territorial sea 12 nm, contiguous zone 24 nm, EEZ 200 nm, continental shelf, innocent passage, and dispute settlement (ITLOS, Annex VII arbitration - relevant to Bangladesh's maritime cases). Jus ad bellum: Article 2(4) prohibition, self-defence under Article 51, anticipatory versus pre-emptive claims, and humanitarian intervention versus R2P.
Traps
Do not confuse signature with consent to be bound; do not call custom "written law"; do not equate R2P with unilateral intervention. Remember diplomatic immunity protects officials from host-state jurisdiction, not from their own sending state.
Worked example
If a treaty is signed but not ratified, the state must refrain from acts defeating its object and purpose (VCLT Art. 18) but is not yet bound.