International law forms the backbone of global governance, shaping how nations interact and resolve disputes. This topic covers the sources that create international law and the core principles that hold the system together.
Understanding these foundations helps you see how international law actually operates: where it gets its authority, what makes a rule binding, and what happens when states break the rules.
Sources of International Law
Article 38 of the ICJ Statute is the standard reference point for identifying sources of international law. It lists three primary sources (treaties, custom, and general principles) along with subsidiary means for determining rules. Keep this framework in mind as you work through the material below.
Customary International Law and Treaties
Customary international law develops when states consistently follow a practice and believe that practice is legally required. Two elements must both be present:
- State practice: Widespread, representative, and generally uniform behavior by states over time. This can include diplomatic conduct, domestic legislation, and how states behave in international organizations.
- Opinio juris: The belief that the practice is carried out because it's legally obligatory, not just out of habit or courtesy. Evidence of opinio juris shows up in official government statements, diplomatic correspondence, and votes on UN resolutions.
If states follow a practice purely out of convenience or tradition but don't consider it legally required, it doesn't qualify as customary law.
Treaties are formal written agreements between states that create binding legal obligations. They can be:
- Bilateral (between two states) or multilateral (among many states)
- Used to codify existing customary law into written form, or to create entirely new obligations
The Vienna Convention on the Law of Treaties (1969) is the key framework governing how treaties work. It establishes rules for treaty formation, interpretation, amendment, and termination. The Convention entered into force in 1980 and applies to treaties between states concluded after that date.
General Principles and Soft Law
General principles of law are legal concepts recognized across the world's major legal systems. They fill gaps where treaties and custom don't provide a clear answer. Examples include good faith, proportionality, and due process.
Soft law refers to non-binding instruments like UN General Assembly resolutions, declarations, and guidelines. These don't create enforceable legal obligations on their own, but they matter because they:
- Shape state behavior and expectations
- Can crystallize over time into binding customary law as states begin treating them as obligatory
Subsidiary sources include judicial decisions and the writings of leading legal scholars. These don't create law directly but help interpret and clarify existing rules. ICJ decisions, while technically binding only on the parties to a case, carry significant weight in legal reasoning and often influence how rules are understood going forward.
Fundamental Principles
Peremptory Norms and Treaty Obligations
Jus cogens (peremptory norms) sit at the top of the international law hierarchy. These are fundamental rules that no state can override or opt out of, even by treaty. If a treaty conflicts with a jus cogens norm, that treaty is void. Recognized examples include the prohibitions on genocide, slavery, torture, and aggression.
Pacta sunt servanda ("agreements must be kept") is the principle that states must fulfill their treaty obligations in good faith. This is codified in Article 26 of the Vienna Convention and is essential for the entire treaty system to function. Without it, treaties would be meaningless.
Erga omnes obligations are owed to the international community as a whole, not just to a specific state. Because they protect fundamental values, any state has a legal interest in their fulfillment. The ICJ identified this concept in the 1970 Barcelona Traction case, citing the prohibitions on aggression and genocide and the protection of basic human rights as examples.
State Sovereignty and Legal Conviction
State sovereignty is the foundational principle of the entire international legal system. It means each state has exclusive authority over its own territory and domestic affairs. Other states and international organizations are, as a general rule, prohibited from interfering.
The principle of non-intervention flows directly from sovereignty. It prohibits states from meddling in another state's internal affairs. However, exceptions exist: the UN Security Council can authorize intervention under Chapter VII of the UN Charter when there's a threat to international peace and security, and debates continue over the legitimacy of humanitarian intervention.
Opinio juris, introduced above as an element of customary law, deserves emphasis here because it's what separates a legally binding custom from a mere pattern of behavior. A state might routinely grant diplomatic immunity out of tradition, but opinio juris is what makes that practice a legal obligation rather than a courtesy.
International Institutions and Conventions
International Court of Justice and Dispute Resolution
The International Court of Justice (ICJ) is the principal judicial organ of the United Nations, based in The Hague. It has two functions:
- Contentious cases: Settling legal disputes between states
- Advisory opinions: Providing legal guidance to UN organs and specialized agencies
A critical feature of the ICJ is that its jurisdiction depends on state consent. A state can't be dragged before the Court against its will. Consent can be given through special agreements, treaty clauses that refer disputes to the ICJ, or optional clause declarations under Article 36(2) of the ICJ Statute.
ICJ decisions are binding only on the parties to the specific case and only for that dispute. Still, the Court's reasoning shapes how international law develops and is understood globally.
Beyond the ICJ, other international tribunals handle specialized areas:
- The International Criminal Court (ICC) prosecutes individuals for genocide, war crimes, and crimes against humanity
- The International Tribunal for the Law of the Sea (ITLOS) handles maritime disputes
- Regional human rights courts (European, Inter-American, African) address human rights violations
- The Permanent Court of Arbitration offers flexible, consent-based dispute resolution
State Responsibility and Legal Consequences
State responsibility is the framework for what happens when a state commits an internationally wrongful act. For responsibility to arise, two conditions must be met:
- The conduct must be attributable to the state (carried out by state organs or agents acting in an official capacity).
- The conduct must breach an international obligation the state is bound by.
Once responsibility is established, the wrongdoing state must:
- Cease the wrongful act
- Provide reparation for the injury caused
Reparation takes three forms:
- Restitution: Restoring the situation to what it was before the wrongful act (the preferred remedy)
- Compensation: Covering financially assessable damages when restitution isn't possible or sufficient
- Satisfaction: Addressing non-material harm, such as a formal acknowledgment of the violation or an official apology
Countermeasures allow an injured state to respond to a wrongful act by temporarily suspending some of its own obligations toward the responsible state. These are meant to pressure the wrongdoing state back into compliance. But countermeasures have strict limits: they must be proportionate, reversible, and they can never violate jus cogens norms or fundamental human rights.