What Is International Law?
By the BrainSnail editorial team. How these articles are written and checked, and how to tell us when one is wrong.
International law is the body of rules governing relations between states and, increasingly, the treatment of individuals. The obvious objection is that there is no world government to enforce it, which is a fair point. The more interesting question is why states comply with it as often as they do.
The recognised sources
International law has recognised sources, set out most clearly in the statute of the International Court of Justice. The two main ones are treaties, which are written agreements between states, and customary international law, which arises from consistent state practice followed out of a sense of legal obligation.
General principles recognised across legal systems, judicial decisions and scholarly writing serve as further sources. Notably there is no legislature. International law is made by states agreeing to it rather than being imposed on them.
The main areas
The field has expanded enormously over the last century:
- •The law of treaties, governing how agreements are made and interpreted
- •The law of armed conflict, limiting conduct in war
- •Human rights law, covering how states treat individuals
- •The law of the sea, governing territorial waters and shipping
- •Trade law, administered largely through the World Trade Organization
- •International criminal law, prosecuting individuals for the gravest crimes
How it is enforced
This is the honest weak point. There is no police force and no compulsory jurisdiction in most cases, since the International Court of Justice generally requires states to consent to being sued.
Enforcement therefore relies on other mechanisms: reciprocity, since a state that breaks a rule invites others to do the same to it, reputation and the ability to make future agreements, economic sanctions, and domestic courts giving effect to international obligations. These are weaker than domestic enforcement but they are not nothing.
Why states usually comply
Despite the enforcement gap, compliance rates with most international law are actually high. Trade rules, postal and aviation agreements, diplomatic immunity and maritime boundaries are followed routinely, without drama.
The reason is largely self interest. Most international law solves coordination problems that states genuinely want solved, and a state that becomes unreliable finds it harder to make agreements it needs. Compliance is visible in the boring areas and violations are visible in the dramatic ones, which distorts the general impression.
Where it fails
The failures are real and concentrated where power is involved. Powerful states can violate rules with limited consequence, the Security Council veto blocks action against permanent members and their allies, and international criminal prosecutions have disproportionately targeted weaker states.
Critics reasonably ask whether something unenforceable against the powerful deserves the name law at all. The usual response from international lawyers is that it functions as law most of the time in most areas, and that a system working imperfectly in the hardest cases is different from a system that does not exist.
How international law reaches individuals
For most of its history international law governed states alone, and individuals had no standing in it whatsoever. That changed substantially after the Second World War.
The Nuremberg trials established that individuals could be held personally responsible for crimes under international law, rejecting the defence that they were following state orders. Human rights treaties then gave individuals rights they could invoke, and some regional systems allow people to bring cases directly. The International Criminal Court, established in 2002, prosecutes individuals rather than states, though several major powers have not joined it.
The takeaway
International law is built from treaties and customary practice rather than legislation, it lacks centralised enforcement and relies on reciprocity and self interest, and it works well in routine areas while struggling exactly where powerful states are involved.