The Athenian general Thucydides fought in the Peloponnesian War, watched it destroy the classical Greek world he had grown up in, and then spent the rest of his life writing the first serious work of political history. In its opening pages he offers a single-sentence explanation of why the war happened: 'What made the war inevitable was the growth of Athenian power and the fear that this caused in Sparta.' Twenty-four centuries later, a Harvard political scientist named Graham Allison took that sentence, tested it against the historical record, and turned it into the most-cited warning about US–China relations in the twenty-first century. His book, 'Destined for War' (2017), popularised the phrase 'Thucydides's Trap' and put it in front of every foreign minister and every general — including, reportedly, Xi Jinping himself, who has referenced the concept in speeches.
Allison and his team at the Harvard Belfer Center went through the historical record since 1500, looking for instances in which a rising power seriously challenged an established one. They found sixteen. Twelve ended in war — Spain versus Portugal, Britain versus France, Germany versus Britain (twice), Japan versus China, Japan versus Russia, and so on. Four ended without major war — Portugal peacefully ceded primacy to Spain (arguably), the United States rose past Britain in the late nineteenth century without a shot, Germany rose again peacefully within a European Union framework after 1990, and the Soviet Union rose against the US without direct combat. Twelve out of sixteen is not a prophecy — Allison is careful to insist on that — but it is a probability distribution, and the numbers are not comforting for anyone hoping the twenty-first century will be an exception. The base rate of great-power transition is bloody.
The archetypal case is Britain and Germany between 1870 and 1914. In 1870, Britain was the world's dominant industrial power, its navy larger than the next two combined. By 1900 German steel production had passed British; by 1910 total industrial output had followed. Under Kaiser Wilhelm II, Germany embarked on the Tirpitz naval programme — a deliberate attempt to build a battle fleet capable of challenging the Royal Navy in the North Sea. Britain responded with the dreadnought race and, less obviously, with a slow but decisive realignment of its diplomacy: the Entente Cordiale with France in 1904, the Anglo-Russian Convention of 1907. Alliances that had once been fluid hardened into two blocs. When a Serbian nationalist shot Archduke Franz Ferdinand in Sarajevo in June 1914, a crisis that in 1900 would have been managed by chancelleries lit the match. Within four years, ten million soldiers were dead and both empires were bankrupt. This is Allison's textbook case — economics, arms race, alliance politics, a match — and it is the case Chinese and American strategists have both been re-reading since 2015.
The most important non-war case in Allison's list is the Cold War. In 1945, the United States controlled roughly half of global GDP, held a monopoly on nuclear weapons, and had suffered relatively little damage at home. The Soviet Union was devastated but had the largest army in Europe and, from 1949, the bomb. Over the following forty-five years, the USSR never overtook the US economically — it peaked at somewhere between 40% and 50% of American output — but militarily it came very close, and in specific domains (heavy tanks, submarine numbers, land-based ballistic missiles) it briefly led. Yet the two powers never fought each other directly. Proxy wars in Korea, Vietnam, Afghanistan, Angola, Nicaragua — dozens of them, millions of deaths — but no direct US–Soviet combat. Nuclear weapons rewrote the calculus of great-power war by making victory in a direct clash impossible to define. Thucydides's trap can be escaped, or at least converted into a colder, longer form of rivalry. It has been done. Whether the mechanism that made escape possible — mutually assured destruction — still works in a world of hypersonic missiles, cyber weapons, and AI-driven decision loops is the open question.
The setup between the United States and China ticks every box in Allison's framework. Since Deng Xiaoping's reforms began in 1978, China has gone from roughly 2% of global GDP to somewhere between 17% and 19% depending on the measure — the fastest sustained economic ascent in modern history. Its navy became the largest in the world by hull count around 2020 and is on track to reach 400 ships by 2030; the US Navy sits at around 290 and is struggling to grow. China now files more patents per year than any other country, graduates more STEM PhDs, publishes more scientific papers, and is the world leader in a growing list of technologies — solar, batteries, EVs, drones, quantum communication, 5G, high-speed rail. Its military modernisation, especially of missile forces and space capabilities, is the fastest of any major power since the Second World War. Whether or not you find this frightening depends on your politics; whether or not it fits the pattern Allison identified is not really debatable. Structurally, this is the classic setup.
One of the most important — and least intuitive — findings in Allison's work is that wars in the trap rarely start over the deepest issue. Britain and Germany did not go to war over industrial supremacy; they went to war over an assassination in the Balkans. The First World War started because European chancelleries had built alliance systems whose logic they no longer controlled, and a local crisis triggered a cascade. Today, the plausible flashpoints for a US–China war are similarly specific and geographically bounded. Taiwan is the obvious candidate: a US-armed democracy 130 km from China's coast that Beijing considers a domestic issue. The South China Sea, where Chinese coast-guard vessels ram Philippine boats around Second Thomas Shoal on a weekly basis, is another. The Korean peninsula, if the North collapses or lashes out, is a third. So is the East China Sea around the Japanese-administered Senkaku/Diaoyu islands. In each case, the underlying rivalry is US–China, but the trigger would be a smaller player and a specific incident. The Sarajevo of the twenty-first century is more likely to be a coast-guard collision than a summit walkout.
The four peaceful transitions in Allison's data set have two features in common. First, leaders on both sides who took the danger seriously and behaved as if avoiding war was a first-order priority — not something to be sacrificed for domestic political points. Second, mechanisms that raised the cost of miscalculation to unacceptable levels: nuclear parity in the Cold War case, deep economic interdependence in the US–UK case, layered institutions and shared democratic identity in the post-1990 German case. The US–China relationship has some of these mechanisms — deep trade ties, though narrowing; nuclear weapons, though the strategic dialogue is thin; the WTO and G20, though both are weakening — but not the personal-diplomacy piece. The Xi–Biden meetings were rare; the Xi–Trump II relationship is still being defined. Whether the twenty-first century joins the shorter, more peaceful list is not a question of destiny. It is a question of choices, made in Beijing and Washington and — this is the underrated part — in Tokyo, Taipei, Manila, Canberra and New Delhi, over the next decade. History suggests the odds are difficult. It also suggests that the difference between the twelve wars and the four peaces has always been made by people who took the trap seriously enough to work around it.
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