When states collide over sea lanes, islands, or invisible boundaries drawn in saltwater, international law becomes the referee. It does not raise a flag or fire a warning shot, but it structures the very language in which maritime disputes are argued, justified, and—sometimes—resolved. Without it, the ocean would remain a frontier of chaos. With it, it becomes a contested but ordered space.

UNCLOS sits at the core of this order. Often called the constitution of the sea, it defines what the sea is—not in myth or might, but in zones, rights, and duties. Territorial seas, contiguous zones, exclusive economic zones, and continental shelves are not political slogans but legal categories with weight and consequence. A rock is not just a rock; under UNCLOS, its ability to sustain human habitation determines whether it generates an EEZ or not. That single distinction can redraw maps and reshape claims.

International conventions transform customary behaviours into obligations. They set expectations not just for states, but for ships, companies, and even individuals. The International Maritime Organization enforces safety, pollution, and training standards through instruments like SOLAS and MARPOL, which feed into broader legal expectations in dispute contexts. A state accused of negligence in protecting its marine environment, or one turning a blind eye to its flagged vessels violating sanctions, cannot hide behind silence—the conventions speak for all parties.

Binding dispute mechanisms create legal theatres where conflicts move from gunboat diplomacy to argumentation. Annex VII tribunals under UNCLOS, the International Tribunal for the Law of the Sea, and the International Court of Justice have all heard cases that go far beyond paper. They interpret ambiguous terms, challenge expansive claims, and—most importantly—provide smaller states with tools to face more powerful adversaries.

Still, law at sea functions within the limits of power. Enforcement is often elusive. A tribunal may rule, but compliance is a matter of state will and international pressure. The South China Sea tribunal ruling in favour of the Philippines exposed this fragility: a powerful legal decision met with strategic indifference. Yet even in non-compliance, the law alters the terrain. It changes the costs of defiance and frames the debate in a legal rather than a militaristic vocabulary.

International law is not a shield that blocks all conflict. It is a current that shapes how disputes flow. Over time, it settles sediment, draws new channels, and filters rhetoric into rules. Its strength lies not in its ability to stop a ship, but in its capacity to make that ship answer to something beyond itself.