In­ter­na­tion­al Law

Before we can say why states obey, we need to see where the rules come from, because they do not descend from any legislature. There is no world parliament passing statutes. International law is built by states themselves, mainly through two channels. The first is treaties — written agreements a state chooses to sign and ratify, from the Geneva Conventions on the conduct of war to the trade rules of the World Trade Organization. A treaty binds only those who join it, which is why the law can look patchy: a country that never signs is simply not bound.

The second channel is stranger and older: custom. When states behave a certain way consistently, and do so out of a sense that they are legally required to, that practice can harden into binding law even with nothing written down. The immunity of diplomats, the freedom of the high seas, the basic rules against torture — much of this grew as custom long before any treaty codified it. Lawyers call the required belief opinio juris, the sense of obligation that turns a mere habit into a rule. It is a curious idea: law made not by command but by the accumulated conduct of the governed.

Here is the part that surprises people: states comply with international law most of the time, and they do it without being forced. The political scientist Louis Henkin put it in a line that has become the field's quiet motto — almost all nations observe almost all principles of international law and almost all of their obligations almost all of the time. The dramatic breaches make the news precisely because they are rare against the background of routine, invisible obedience.

The reason is not conscience. It's self-interest, running through a few durable channels. The first is reciprocity: a state that violates a rule invites others to violate it back. If one government mistreats another's diplomats, its own diplomats become fair game everywhere. The Geneva Conventions on prisoners of war hold in part because each side wants its own captured soldiers protected. The rule survives because breaking it costs the breaker directly.

Step back and international law starts to look like a magnified version of something we live inside every day. Most of the order around us runs not on force but on the same quiet machinery: reciprocity, reputation, and shared interest. We keep promises to people we'll deal with again, honor debts to protect our standing, follow conventions because everyone else does and the arrangement suits us. The police almost never appear. Between states the pattern is only starker, because there the enforcer genuinely does not exist, and yet the cooperation still forms. International law is the clearest proof of how much of the world holds together on incentives rather than threats.

Nicaragua's paper victory in The Hague was not the exception that proves international law hollow. It was the system showing both its faces at once. A court that could reason its way to a verdict but never collect on it; a superpower that lost the argument and ignored it because, on that one question, the cost of cooperation had stopped mattering to it. The same court, in the same decades, settled hundreds of quieter disputes over borders and fishing rights and treaty terms that the parties actually wanted resolved.