More than two months after the start of the Iran war, shipping through the Strait of Hormuz - a key waterway through which more than a third of international oil and gas trade passes - remains dangerous and uncertain. Underscoring this uncertainty, on May 3, 2026, the Trump administration launched "Project Freedom" to help blocked ships pass through the strait. The next day, however, at least two ships were fired upon by Iran.
This is what Vivek Krishnamurthy, an associate professor of law at the University of Colorado Boulder, wrote in an article for The Conversation.
Iran began blocking shipping through the strait on February 28 after the United States and Israel launched a military campaign against the country. By mid-March, Tehran was demanding fees of up to $2 million per ship. In response, the United States imposed what President Donald Trump called a "complete" naval blockade of Iran and subsequently threatened serious economic sanctions on anyone who paid Iran's fees.
Following Iran's example, other countries are now considering using their influence to control key geographical bottlenecks near their coasts. Indonesia proposed imposing tariffs on ships passing through the Strait of Malacca, but later abandoned them. China has also issued warnings against foreign warships passing through the Taiwan Strait.
These events have prompted commentators to sound the alarm about the end of the golden age of freedom of navigation that the United States has guaranteed for more than a century. But as an expert in international law, I know that attempts by states to weaponize their influence over key geographical chokepoints at sea and on land are nothing new. In fact, they
The Danish Roots of Maritime Dues
From the early 15th century until 1857, Denmark required ships passing through the narrow straits connecting the North Sea to the Baltic Sea to stop at the port city of Helsingør—or Elsinore, as William Shakespeare called it in Hamlet—and pay a fee before continuing.
At their peak, these maritime dues generated nearly 10% of Denmark’s national income. The tolls irritated the naval powers of the time, but Denmark was able to collect them easily thanks to the narrow strait of Øresund, which is less than 3 miles wide at Helsingør.
They were eventually abolished not by war but by diplomacy, largely led by a rising sea power with a strong interest in open sea routes: the United States.
In an effort to expand its trade with Prussia, in 1843 the administration of President John Tyler notified Denmark that the United States refused to pay the strait tolls, as they had no basis in international law. Rumors circulated that the United States was prepared to enforce its refusal by force.
After years of uncertainty, the fate of the strait tolls was decided by the Copenhagen Convention of 1857. Denmark agreed to permanently abolish the tolls in exchange for a one-time payment from the major trading nations. The principle of free navigation of the world's oceans has largely survived since then, in part because of subsequent efforts by the United States to enforce those freedoms against those who sought to restrict them.
How did the law develop?
The Danish Agreement reflects a broader body of law—the law of transit—that has developed alongside an international system of sovereign states over centuries.
Its basic principle is that, when convenience or necessity so requires, a state must allow people, goods, and ships of other states to pass through its territory on voyages that begin and end elsewhere. This principle has deep roots in American and international legal history: Thomas Jefferson used it in negotiations with Spain, which then controlled Louisiana, to secure the right of the United States to navigate the Mississippi River.
Guarantees of free transit have been a feature of every major international order since the Congress of Vienna ended the Napoleonic Wars in 1815. In each case, however, these guarantees have come under pressure as the order that created them has weakened.
Before World War I, restrictions on transit rights multiplied throughout Europe. The League of Nations, the predecessor of today's United Nations, made strengthening transit rights a top priority in the 1920s. However, these agreements fell apart with the rise of fascism in Europe and Asia, and regimes from Nazi Germany to Imperial Japan abandoned their international legal obligations.
The order established after World War II affirmed transit rights - through maritime law, trade agreements, and laws regulating civil aviation - and they remained in force for decades.
In its first case, decided in 1949, the International Court of Justice clarified the basic legal principle of international straits: any waterway useful for international navigation between two high seas is open to ships of all states.
The United Nations Convention on the Law of the Sea confirmed this rule by stipulating that states may not levy duties on ships passing through straits in their waters. Although neither Iran nor the United States has ratified the convention, the United States recognizes its freedom of navigation provisions as binding on all states.
Iran’s tolling in the Strait of Hormuz violates the fundamental legal principle that states cannot use their geographical advantages to extort foreigners who must pass through their land or maritime territory. The U.S. and Israeli military campaign that has provoked Iran’s response also violates the rules of the UN Charter on the use of force.
Such problems are not limited to the Strait of Hormuz. Indeed, trade law, security commitments, and norms prohibiting unilateral border redrawing are at stake.
In this broader context, China’s warnings against military passage through the Taiwan Strait and Indonesia’s test passage through the Strait of Malacca are not isolated provocations. These are symptoms of the same fundamental phenomenon: the international order is losing the shared commitment that often ensured the application of its rules.
In January 2026, Trump told the New York Times that he did not need international law and that his own moral judgment was the only limit on American foreign policy. Around the same time, Canadian Prime Minister Mark Carney warned that the American-led international order was "fading".
The Strait of Hormuz is where these trends are now colliding—to the detriment of billions of people around the world and destroying the idea of an international order based on law rather than the brutal use of force.