By 1806, aside from a relatively brief period of peace following the 1802 Treaty of Amiens, Britain had been at war with revolutionary and then Napoleonic France for a decade and a half. The crushing British naval victory at Trafalgar over the Franco-Spanish fleet in late October 1805, and the equally crushing French victory on land at Austerlitz over the Austrians and the Russians just six or so weeks later, had reinforced the broad strategic parameters of the contest. Britain was utterly dominant at sea and France equally dominant on land in the continent of Europe; the whale faced the elephant. With neither side able to directly strike at the other, both turned increasingly to forms of economic warfare.

For Britain, this meant leaning into the strength of her naval power. The French navy and most of her merchant marine was bottled up in her ports, hemmed in by a tightly maintained close blockade. Vessels carrying French goods were liable to be seized. French overseas trade was choked off. For Napoleon’s France, following the Berlin Decree of 1806, this meant the so-called Continental System, which closed European ports to British vessels and banned all trade in British goods, including those produced in British colonies.

And yet in 1809, and again in 1810, when British harvests were poor and Europe had a surplus of grains, the French Emperor was more than happy to grant export licenses allowing wheat to be sold to his enemy.

To modern eyes, agreeing to export much needed food to an enemy during wartime – especially at a time of mutual blockade – may appear strange. But in the framework through which Napoleon thought about the nature of the economy and economic warfare, it made perfect sense. This was the era of mercantilism.

Exports, by this way of thinking, added to a nation’s strength and its ability to make war by causing an inflow of bullion and other precious metals in return. By contrast, imports – which would have to be paid for via precious metals – were something which weakened a state and were to be, if possible, avoided. The logic of the Continental System was to crimp British exports and so harm the United Kingdom’s ability to build up a stock of bullion. Exporting foodstuffs in 1809 and 1810, by this way of thinking, drained the enemy’s bullion reserves and diminished their power. Economic warfare then, in the late-18th and early 19th century, was not so much about denying an enemy access to vital resources (and few things are as vital as food) and more about degrading their ability to pay to continue fighting.

By the time of Europe’s next major continent-spanning war between the great powers, a century later, things had changed. While retarding an enemy’s ability to export and finances still played a role, much more emphasis was placed on denying crucial imports in an effort to directly collapse a country’s ability to make war. For Britain, this once again meant relying on the Royal Navy to enforce a blockade on her continental enemy. As the war went on, ever tighter rules were put in place, restricting Germany’s ability to import – and export – via her neutral neighbours. By 1918, German imports – adjusted for changes in prices – had fallen by 60 per cent from their pre-war levels and exports by more than 70 per cent.

Imperial Germany, though, had access to a weapon Napoleon’s France did not: the submarine. Submarine warfare against Britain, and neutral shipping visiting British ports, proceeded in something of a stop-start pattern. In February 1915, the Germans announced that the waters around the United Kingdom would be regarded as a war zone, that all enemy ships in such water would be sunk without warning and, furthermore, that they could not guarantee the safety of any neutral vessels in those waters. Just eight months later, in September 1915, unrestricted submarine warfare was called off in the face of rising diplomatic pressure from the neutrals – notably the United States, following the death of 128 Americans when the liner Lusitania was torpedoed in May 1915.

In December 1916, though, with the war still dragging on and both sides looking for routes to victory, Admiral Henning von Holtzendorff penned one of the war’s most important memorandums. Improvements in both the quantity and quality of Germany’s U-boat fleet handed the Reich, in his view, a potentially war-winning weapon. Unleashing it once again could sink around 600,000 tons of Allied shipping monthly and, in Holtzendorff’s view, end the war within six months as Britain ran out of food. The plan went into effect the following February and by April 1917 shipping losses were running at over 800,000 tons per month.

Economic warfare would play a decisive role in the Great War, although not in a way that many contemporaries would have expected. Britain, which had embraced free trade by the mid-19^th century, and which imported around 60 per cent of its calories, proved able to weather the long months of submarine warfare. The introduction of a convoy system to protect shipping eventually cut losses to a more acceptable level and no Britons died of hunger over the course of the war. In Germany, though, which imported fewer than a quarter of its calories before the war, several hundred thousand perished from malnutrition. Meat consumption, to give but one example, was running at 80 per cent of its 1913 level in import reliant Britain by 1918, but just 20 per cent of its 1913 level in Germany.

Separating out the impact of the British-led blockade and the general chaotic way in which Germany managed its own domestic war economy between 1914 and 1918 is not straightforward. The best modern estimates suggest that between one fifth and one third of the decline in German food supply over the course of the war was a result of the blockade, with the rest accounted for mostly by the mass mobilisation of men, horses and the chemicals once used in fertilisers (and now required to make explosives) away from agriculture.

Contemporary observers though were impressed by the seeming efficiency of the blockade, and economic warfare in general, which had helped to break the deadlock on the Western Front. The League of Nations, it was hoped, would be able to employ such tools as its primary form of coercion against violent powers. The economic weapon would be collectively wielded to ensure peace. Sanctions, though, failed to prevent Italian aggression in Abyssinia or Japanese expansionism in East Asia.

During the Second World War, economic warfare spread even further, mostly notably through the use of co-called strategic bombing. Heavy and sustained campaigns of air attack were designed to destroy factories and transport infrastructure and directly lower war production and the ability to fight.

Years of heavy Anglo-American bombing of Germany contributed to the Allied victory in Europe, although rarely in the ways that airpower evangelists or targeting officers expected. Take, as one example, the issue of ball bearings. For anyone who had studied the input-output tables of German industry as closely as Allied planning staffs, ball bearings appeared to be absolutely critical to all sorts of military technology. Everything from tanks to fighter planes to machine guns relied on ball bearings in some regard. What is more, German ball-bearing production was relatively concentrated in a handful of factories. The lesson was obvious: knock out those factories and German war production would collapse.

A series of costly raids in 1943 did succeed in destroying around half of Germany’s ball-bearing production facilities, but, as the postwar Strategic Bombing Survey was disappointed to report, this had almost no effect on Germany’s ability to fight the war. Instead of war production collapsing, Germany was able to run down existing stockpiles and, in many cases, to substitute away to a different component.

A recent book looking back at several centuries of the history of economic warfare and sanctions, edited by the economists Stephen Broadberry and Mark Harrison, points to some useful general conclusions. The most significant of which is that economic warfare during an actual shooting conflict and economic sanctions in peacetime are best seen as a complement to other activities and tools of coercion rather than an alternative. Economic warfare works when coupled with direct warfighting, while economic sanctions need to be employed alongside credible deterrence through investing in warfighting capacity. A trade embargo or financial sanctions alone have rarely changed the behaviour of a state. Indeed, one study, published in 2007, looked back at 174 uses of sanctions between 1915 and 2000 (162 of those taking place after 1945) and found that such sanctions achieved their stated aims in only one third of all cases. The economic weapon was mostly likely to work in cases where goals were clearly set, the target state was already economically weak and where there was little history of antagonism between the parties before their use.

A key insight from the work of Harrison and Broadberry, drawing on work first published by the economist Mancur Olson in the 1960s, is that there is rarely such a thing as a ‘strategic commodity’. Instead, there are only strategic uses. People need, for example, to be fed. But they do not necessarily have to be fed by grains and meats shipped in from the Americas as was the case for many Britons in the 1910s. Destroying half of Germany’s ball-bearing production in 1943 did not cause the collapse of the entire war economy, but it did impose real and material costs – the costs of adaption and of using less efficient components – on the German economy. In most cases, the costs of this sort of economic warfare were ultimately shifted onto the civilian population, as the war effort took priority.

Economic warfare then, and sanctions and blockades in peacetime, are a tool that works slowly, cumulatively imposing ever higher costs on the enemy.

The economic warfare waged against Russia since 2022 by the western powers is an excellent example. Following the imposition of a tough – and one regularly tightened since – sanctions package on the Russian economy after it invaded Ukraine, some analysts became overexcited. The most excitable asked whether Russia faced a ‘1998 moment’, the year of a major government default and devaluation, or even a ‘1917 moment’, as when the Tsarist regime collapsed amid the pressure of war and economic crisis.

It is now obvious, four years on, that neither has occurred. But the sanctions have had an impact and exactly the impact that should have been expected: the slow accumulation of the costs of adaptation. In 2023, the Russian economy, fuelled by war related spending, grew by more than four per cent. Last year, it expanded by just 1.5 per cent and this year that looks set to slow further to around one per cent. Meanwhile, inflation and interest rates have soared, living standards have been severely squeezed and non-war related industries starved of investment.

Much has been made of Russia’s ability to side-step western restrictions by rerouting imports through, say, Kazakhstan. But the overall volume has been severely limited. Meanwhile, the loss of access to funds (frozen in the West) coupled with Ukraine’s ‘kinetic sanctions’, or targeting of Russian shadow fleet vessels and oil and gas export facilities, has damaged its ability to export. Russia’s prosecution of the war has been severely hampered and that damage will keep building over time. In this case, economic warfare by the West has been acting as a complement to actual war-fighting by Ukraine.

The war in the Gulf has also been accompanied, and in many ways preceded, by the tools of modern economic warfare. The United States began ramping up sanctions on Iran in the 2000s at a time when it was already fighting wars in Iraq and Afghanistan and did not wish to become involved in a third. Two decades of sanctions have caused severe damage to the Iranian economy and to civilian life. To grasp the extent of the inflationary pain, one need look no further than Iranian bank notes. In 2005, the largest denomination note was worth 10,000 rials. By 2020, one million rial notes were circulating and this year has seen the issuance of a ten million rial note.

And yet, two decades of intense peacetime economic warfare, waged and led by the most powerful economy on earth, may have been enough to cause widespread inflation and real civilian pain – enough to prompt major unrest in January – but it still left a country capable of sustaining a bombardment of drones and missile attacks across the wider region throughout weeks of heavy fighting.

Iran’s effective closure of the Strait of Hormuz, in an attempt to put pressure on the United States to make peace, is a form of asymmetric warfare waged against the entire global economy. But, like all economic warfare, the results are unlikely to be swift.

In 1916, the German High Command convinced itself that unrestricted submarine warfare could end the Great War in months. In 1943, many US Army Air Force officers believed that destroying ball-bearing production could deliver a knockout blow to the Third Reich’s war economy. Napoleon hoped that his Continental System would force Britain to the negotiating table. Similar claims have abounded in recent weeks, with op-eds and TV news show guests eager to argue that a US seizure of Kharg Island (through which most Iranian crude exports flow) or a US naval blockade (now in place) could quickly collapse Iranian government revenues and force the regime either into admitting defeat or collapse. That, though, is not how economic warfare works. There is no ‘one simple trick’ that causes an economy to collapse and a war effort to instantly falter. There is no easy short cut to victory. Economic warfare is a powerful tool of coercion, but one that works slowly.