The scenario that keeps Western planners awake is easy to describe and, it turns out, almost entirely unstudied: Russia moves on a Nato member while China moves on Taiwan, The Atlantic reported on August 17.

Asked what the West would actually do if Russia and China opened two fronts in Europe and Taiwan simultaneously, senior military figures and strategists mostly said they did not know, - and several expressed embarrassment at how little work has been done on it.

"Let's just say this is the scenario we're currently not ready for," said Florence Gaub, director of the research division at the Nato Defence College in Rome. Alliance strategists are "keenly aware" of the gap, she said, and have not filled it.

Admiral Rob Bauer, who chaired Nato's Military Committee until he retired last January, said he was aware of no concerted effort inside the alliance to prepare for what he called the worst-case scenario. "What are we going to do? Who's getting which troops?" he asked in an interview with the US magazine. "I think it would be wise to think that through."

This matters now because the assumptions that made the scenario dismissible have quietly stopped holding. It used to be filed somewhere between a loose nuclear weapon and an alien invasion, on the reasoning that a conspiracy that large could not be hidden and satellites would give ample warning. What has changed is not the warning time but the balance of what would follow it.

Mark Montgomery, a retired US Navy rear admiral who has run war games on the question, said the last serious study of a two-front war against Russia and China was roughly 15 years ago. "It didn't go well," he said: the US lacked the stockpiles and industrial capacity to fight on two fronts for long, and could not count on allies to make up the difference.

"Every one of those metrics has gone down. None of them has gotten better," Montgomery said. European defence spending has risen under US pressure, "but their forces have not yet shown improvement."

The other side's metrics moved the other way. Russia has not achieved its objectives in Ukraine but has put an enormous industrial base on a war footing and learned drone warfare the hard way. China, which builds most of the world's drones, has overtaken the US in warship numbers and long-range missiles. The two hold regular joint drills under what their leaders call a "no-limits" partnership, and China has become the main supplier of technology to Russia's weapons industry while buying the oil and gas that keeps its economy running.

Meanwhile the US is stretched. It remains bogged down in Iran, having pulled ships and aircraft out of Asia and Europe to backfill the Middle East, and an estimated two-thirds of its advanced air-defence missile stockpile has been consumed since February - the same shortage that has left Ukraine's interceptors running dry. Donald Trump's repeated threats against Nato have done the rest.

Nato Secretary General Mark Rutte has said the quiet part out loud, if only briefly. "China is looking at Taiwan," he told a German newspaper in December. "And I am convinced that if China takes military action there, it will pressure its junior partner, Russia, under Putin's leadership, to keep us busy here in Europe."

The most detailed public work on the problem is being done not by a major Western think tank but by the European Values Center for Security Policy, a small institute in Prague, which has run around 20 rounds of dual-theatre war games since 2024. Its director Jakub Janda said the results are consistently alarming for Europeans: in almost every scenario the US prioritises China and shifts resources out of Europe, leaving Nato allies to hold off Russia alone.

One of Janda's scenarios does not begin with a shot at all. China bans exports of raw materials to Europe's defence sector and holds the embargo for five months, until European weapons factories run out of inputs. Only then, with full access to Chinese supplies, does Russia invade.

The obstacle to studying this is partly bureaucratic. Tabletop exercises are built for clarity - two teams, tight rules, one theatre - and "multi-crisis environments" break the format. Eric Heginbotham of MIT's Security Studies Program said the topic is discussed more than it used to be. "It's complicated, to be sure, but I don't think it is too complicated to study. I just don't believe that anyone has done it."

Some planning is happening at the European end. Bild has reported a three-stage Nato response plan for a Russian attack on the Baltic states: repelling incoming missiles and drones while striking Russian military targets including in Kaliningrad; building an "autonomous defence zone" of drones and ground robots along the borders with Russia and Belarus; and, at a later stage, deep strikes inside Russia against airfields, defence plants, bridges and rail hubs. Nato wants it in place by the end of 2027.

That is a plan for one front. The gap Gaub and Bauer describe is what happens when a second opens at the same time - and the historical record on this particular failure mode is not encouraging. Stalin had warnings from his own generals and spies before June 1941 and refused to believe them. Washington did not prepare for Pearl Harbor. Europe split into two alliances before 1914 and nobody forecast what their collision would cost.

"The indications were clear that they would clash, and we just weren't ready for it," said David Santoro, president of the Pacific Forum in Hawaii, who ran a 2023 exercise in which China attacked Taiwan while North Korea invaded South Korea. "We were struggling to keep up and divide labour. And we weren't even talking about Europe."