The Hill reports that Houthi rebels have attacked two Saudi oil tankers in the Red Sea and declared a blockade of the Bab el-Mandeb Strait — one of the narrowest and most consequential passages in the world's trading system. It is, in the language of our day, a chokepoint. In my own language, it is a place where the security of exchange depends entirely on who commands the water.

I argued in The Wealth of Nations that the great gains from trade — the division of labor, the specialization of production across nations — are only realizable when goods can move. A commodity grown in Arabia, refined in one port, consumed in another, passes through many hands and many miles. Each mile of that passage is a link in a chain; sever one link and the whole chain fails. An oil tanker sitting at anchor under threat is not merely a financial loss to its owners; it is a tax — imposed by violence — on every consumer downstream who heats a home or drives a vehicle with fuel that cannot arrive.

This is precisely the category of problem I assigned to the sovereign rather than to the merchant. Defense of the sea-lanes is a public good in the strictest sense: its benefits cannot be confined to those who pay for it, and its absence harms everyone who trades. No individual shipowner, however wealthy, can pacify a strait. That requires collective provision — what I called one of the three legitimate duties of the sovereign — and when it fails, the cost is borne not by admirals and ministers but by the workman who pays more for goods, and the consumer who receives less.

There is a second lesson here, one that touches the moral foundations of commerce. The Houthis' declared blockade is, in form, an act of coercion — the substitution of force for the mutual advantage that voluntary exchange requires. I have always held that the moral foundation of commerce is sympathy: the capacity of parties to imagine themselves in one another's position, to honor a contract because they grasp what its breach would mean to the other. Blockade is the negation of that sentiment. It says: your loss is my instrument. No honest market can be built on such a footing.

Where does this leave us, institutionally? The Bab el-Mandeb is not a river running through a single sovereign's territory; it is an international passage whose security is a collective problem. History suggests — and here I reason by inference, not recollection, for these events are beyond my own era — that such passages have been kept open only when some combination of naval powers treats their defense as a shared interest. When that coalition frays, or when a regional conflict provides a party with both motive and capability to close the strait, commerce pays the price. The proper remedy is not for each merchant to arm his own vessel, but for the nations that benefit from open trade to construct, maintain, and where necessary enforce the institutional framework that makes passage safe. That is not a counsel of war; it is a counsel of honest accounting about what trade actually costs to sustain.