If outsiders walked through someone's yard without the owner's permission, they could be charged with trespassing. In international relations, too, violating another country's territory, airspace, or territorial waters is an illegal act that invites disputes. But there is an exception. Ships of any nationality may freely pass through another country's territorial waters, provided they do not "prejudice the peace, good order, or security" of that state. Even warships may traverse foreign territorial waters if their purpose is simple passage rather than military action. This is a right guaranteed by international law and custom — the so-called "right of innocent passage."
The right of innocent passage was first codified in international conventions and law beginning in 1958. At the time, participating nations at the first United Nations Conference on the Law of the Sea adopted four conventions to resolve maritime sovereignty disputes. Among them, the Convention on the Territorial Sea and the Contiguous Zone was the first to contain provisions defining and guaranteeing innocent passage. The parties later consolidated and supplemented the four treaties into a single convention through subsequent conferences. That is the United Nations Convention on the Law of the Sea (UNCLOS), often called the constitution of the oceans. South Korea ratified this convention — which entered into force in 1994 — two years later, explicitly securing the right of innocent passage. This more firmly opened the maritime trade routes that are the lifeline of the Korean economy.
Iran recently blockaded the Strait of Hormuz while at war with the United States, and its parliament passed a plan to impose "maritime transit tolls" on ships. This is an act that shakes the foundation of innocent passage rights. Iran signed UNCLOS but never ratified it. Nevertheless, guaranteeing the right of innocent passage is a duty of strait-bordering states under customary law. The International Court of Justice ruled in 1949 that, under customary law, coastal states cannot obstruct innocent passage for international navigation in straits connecting areas of the high seas. That ruling was issued on the premise of "peacetime."
The government must meticulously explore ways to secure innocent passage under customary law once a ceasefire or peace settlement between the United States and Iran restores peacetime conditions to the Strait of Hormuz. This is because Iran may impose maritime transit tolls in earnest to fund post-war reconstruction. South Korea must also prepare diplomatically to prevent similar situations in the South China Sea and significantly strengthen its naval capabilities to a combat-ready level so it can escort Korean shipping fleets in the event of a crisis.