Fertilizer's Chokepoint Problem Is Older Than the Oil Age
When Iran closed the Strait of Hormuz, roughly one-third of the world's fertilizer trade stopped moving. The disruption was immediate. The strategic logic behind it, however, is nearly two centuries old.
Edward D. Melillo, an environmental historian writing in The Conversation, traces that logic back to the 19th century, when seabird guano — not petroleum — was the resource that fed nations and built empires. The parallels to today's crisis are not accidental.
The first global fertilizer commodity
Before synthetic ammonia, farmers across Britain, central Europe, Virginia and the American South depended on dried bird excrement shipped from rocky Pacific and Caribbean islands. Rich in nitrogen and phosphorus, guano transformed agricultural productivity at a moment when industrializing cities were stripping rural soils of nutrients faster than local systems could replenish them.
According to Melillo, commercial interest in guano surged in the 1840s after agricultural chemist Justus von Liebig demonstrated that crop growth depended on replacing nutrients removed from the soil. Peruvian guano — accumulated over millennia by guanay cormorants, Peruvian boobies and pelicans on the nearly rainless Chincha Islands, 13 miles offshore — suddenly became a globally traded strategic asset.
Melillo calls this trade 'the first Green Revolution,' predating synthetic ammonia by decades and laying the foundations for the chemically intensive agriculture that followed World War II.
Sovereignty follows supply
The United States drew the obvious conclusion. The Guano Islands Act of 1856 — still active law — authorized American citizens to claim uninhabited islands containing guano deposits on behalf of the federal government. The statute effectively extended U.S. territorial reach across the Pacific and Caribbean in direct pursuit of agricultural inputs.
The law remains on the books today, a 169-year-old reminder that food security has always been a national security question, and that Washington has historically been willing to assert sovereign claims when critical supply chains are threatened.
Today's vulnerability is structural
The Hormuz closure did not create the fertilizer problem — it revealed one already in progress. According to Melillo, even before the Iran conflict, Russia's invasion of Ukraine had disrupted global nitrogen fertilizer markets tied to natural gas. Sanctions on Belarus had unsettled potash trade, a principal source of potassium for agriculture. China had restricted phosphate exports to stabilize domestic prices.
Three of agriculture's four principal nutrient inputs — nitrogen, potassium and phosphorus — were already under geopolitical pressure before a single tanker was turned back at Hormuz.
The market has already voted
The numbers come first, and the numbers say that modern food production is built on supply chains that run through adversarial or unstable jurisdictions. That is not a climate story or a trade technicality. It is a sovereignty problem.
Free enterprise cannot function when the inputs to basic food production are subject to the veto of foreign governments or the closure of a single strait. The 1856 Guano Islands Act was an imperfect answer to an earlier version of this problem — but it was at least an answer. The question for American policymakers today is whether the strategic imagination that produced that law still exists in Washington, or whether the administrative state has grown too comfortable managing scarcity to bother preventing it.
