For centuries the so-called cannon shot rule determined who controlled the seas. The legal concept, codified by Dutch jurist Cornelius van Bynkershoek in 1702, was simple: The distance a cannonball reached from shore set the maritime boundary of a coastal state.1 Fast forward 300-plus years and little seems to have changed, only the weapons. Today, missiles and drones draw the limits.
On Tuesday night, the US and Iran agreed a tentative two-week ceasefire that pauses a six-week conflict that many have already — and rightly — called the War of Hormuz because of the central importance of the stretch of water that goes by that name. What follows will demand the ultimate feat of linguistic gymnastics from diplomats and negotiators working on a lasting peace: They’ll need to square a circle over how the strait is governed, letting both Washington and Tehran claim they got what they wanted.
One thing is clear: No matter how one dissects the American and Iranian statements about the ceasefire, the strait’s status has changed. What was a free waterway before the hostilities began is today — at the very least — a controlled one. Its future is up in the air, and with it the seaborne passage of a fifth of the world’s oil and liquefied natural gas supplies.
Can the strait return to its prewar status, effectively subject to the United Nations Convention on the Law of the Sea, allowing free passage, unimpeded by tolls and fees? Maybe, but I doubt it. Neither Iran nor the US has ratified that UN treaty, even if both effectively followed some of its provisions. So both are free to try to rearrange things.
The solution, pending the coming days of US-Iran negotiations, can probably be found in treaties that govern other maritime chokepoints, notably the Bosporus and the Danish straits. They are examples that preserve free navigation while giving the coastal states bordering a waterway — Iran and Oman in the case of Hormuz — rights over it. Tolls can be called something else that’s politically acceptable; say, pilotage services or oil-spillage prevention fees. And Iran can get what it wants on paper, but in practice never see a dime if most shipping shifts toward Omani waters.
President Donald Trump insists he wants “complete, immediate, and safe” navigation via the strait, but he also reposted on social media an Iranian statement that indicated that passage would, for now, be limited and under the control of its military. As of Wednesday morning, few vessels had crossed the strait and Tehran’s message was clear: Its permission is needed to go ahead.
To bridge the gap, it helps to look at the history of some of the world’s most important sea chokepoints, and the laws that govern them.
The Treaty for the Redemption of the Sound Dues, signed in Copenhagen in 1857, regulates to this day navigation through the Danish straits, another critical waterway for oil and refined products. It states that Denmark should “supervise” the pilotage service through the straits, giving it effective oversight. Nonetheless, those services aren’t mandatory. On paper Denmark controls the passage; in reality it has limited rights.
The Bosporus, a chokepoint for a large amount of oil and agricultural commodities, is another useful template. The strait is governed by the so-called 1936 Montreux Convention. Turkey explains the meaning of the treaty in a way that could help talks around Hormuz. The straits, Ankara says, enjoy “freedom of passage” but in a way that “cannot be interpreted to mean ‘free and unregulated’ passage.” Incongruent? No, just the art of diplomacy. Turkish authorities regulate the traffic and collect some fees for pilotage services.
For Iran, keeping some control over the strait is crucial. It reinforces deterrence against future attacks by Israel and the US. But Tehran doesn’t need to exert physical control over the waterway to keep its leverage over the global economy. The last six weeks have been a lesson for everybody — the Americans uppermost — in the geopolitics of energy. This hard-won knowledge won’t go away regardless of the outcome of peace talks.
The Islamic Republic has a new sense of its own strategic power, one to potentially match a nuclear arsenal. Iran assumed the waterway gave it a lever over the international economy, but its effectiveness was unproven. Tehran didn’t know whether it would actually be able to close the strait at a time of war, and if so for how long. It didn’t know how the US and the global community would respond, and how the oil and gas markets would react. Now, it knows. Nothing that is negotiated will change that.
And yet, Iran isn’t alone in learning a crucial geopolitical lesson. Its neighbors have, too, and that will gradually weaken Tehran’s strategic advantage. Saudi Arabia and the United Arab Emirates managed to circumvent the chokepoint to a limited degree via their bypass pipelines. Riyadh and Abu Dhabi are almost certain to double down, expanding those emergency conduits further.
Kuwait would doubtless join forces with the Saudis to build its own bypass pipeline. Iraq would struggle with the expense, but it has every incentive to rebuild its old strategic pipeline that let it move oil from the south to the Mediterranean via Turkey.
Iran’s stranglehold over energy supplies will therefore loosen over time. Five years from now, the Persian Gulf will have far better bypass options than it does today. No matter what the US and Iran agree over the future of Hormuz, the strait’s status will change. But the waterway will never be as critical to the global economy as it was when the fighting started six weeks ago.
1. The principle is often summarized as "terrae dominium finitur ubi finitur armorum vis" (The dominion of the land ends where the power of arms ends).
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