Western military planners do not seem eager to talk about their nightmare scenario, much less prepare for it. But they tend to agree on how it would begin: a coordinated, near-simultaneous attack on opposite sides of the planet, in which Russia targets a NATO member in Eastern Europe while China makes its move against Taiwan. The U.S. military would need to react on two fronts at once—three if it remains at war in the Middle East.Until recently, this possibility sat at the more outlandish end of the threat spectrum, somewhere between a loose nuke and an alien invasion. Synchronized attacks would require a conspiracy too big for Beijing and Moscow to hide. Satellites would see their forces getting into position, giving the United States and its allies time to rally their defenses.About a year ago, General Alexus Grynkewich, the top NATO commander in Europe, issued a rare public warning about the risk of a two-front war against Russia and China, and he called on European allies to help the U.S. prepare. But when I asked a range of military experts and strategists what the West would do in such a situation, the responses rang surprisingly hollow. Most of them expressed bewilderment and a bit of shame about how little has been done in recent years to study this risk in detail.“Let’s just say this is the scenario we’re currently not ready for,” Florence Gaub, the director of the research division at the NATO Defense College, one of the alliance’s main academies for officers, in Rome, told me. NATO strategists remain “keenly aware” of this gap in their planning, Gaub, who specializes in the forecasting and analysis of future threats, said. But they have not taken steps to fill that gap.Even as Russia and China have intensified their military cooperation, the West has held only a few low-profile exercises to analyze what would happen if the two launched a joint attack. Public discussion of this possibility has been remarkably muted among Western experts and military brass, who seem to lack the theoretical frameworks to process such a calamity and game out a response.Mark Montgomery, a retired rear admiral of the U.S. Navy and a frequent participant in high-profile war games and strategic-planning exercises, told me that he and his colleagues last studied the idea of a two-front war against Russia and China roughly 15 years ago. “It didn’t go well,” he said.Back then, the exercises showed that the U.S. did not have the weapons stockpiles or the industrial capacity to sustain a lengthy period of fighting on multiple fronts, and it could not rely on its allies to pick up the slack. Since then, Montgomery said, “Every one of those metrics has gone down. None of them has gotten better.” Under pressure from the Trump administration, U.S. allies have increased their defense spending. “But their forces have not yet shown improvement.”The other sides have. Although Russia has been failing to achieve its objectives in the war in Ukraine, it has succeeded in shifting its enormous industrial base onto a war footing, and formerly civilian factories now aid in the production of missiles and tanks. The Russian experience in Ukraine has also made its forces adept at drone warfare. China, which produces most of the world’s drones, has not fought a war in decades and suffers from corruption in its upper ranks. But it has overtaken the U.S. in the number of warships and long-range missiles in its arsenal. Russia and China have also built stronger ties between their militaries under what their leaders describe as a “no-limits” partnership.From their vantage point, the window of opportunity to strike the West might never have looked more tantalizing. The U.S. remains bogged down in Iran, having pulled a lot of its ships and aircraft out of Asia and Europe to backfill its forces in the Middle East. An estimated two-thirds of the American arsenal of advanced air-defense missiles has been depleted since February, and Donald Trump’s persistent insults and threats against NATO have turned the rift between the U.S. and its allies into a yawning chasm.For most of his tenure as Russia’s president, Vladimir Putin has aspired to dismantle NATO, and its current moment of weakness offers him a rare chance to achieve that goal. He has already started testing its defenses. NATO members in Eastern Europe, such as Romania, Poland, and the Baltic states, have seen repeated violations of their air space by Russian drones, missiles, and fighter jets. Earlier this month, German authorities found a suspected Russian drone loaded with explosives at an airport in Leipzig, apparently preparing to blow up a Ukrainian cargo plane over NATO territory.The most recent U.S.-intelligence assessments have reportedly concluded that Russia could try to test NATO’s resolve in the next few years, using a cyberattack or a small-scale incursion against a member of the alliance. Such a gambit would be more likely to succeed in weakening NATO if Russia timed it to coincide with a Chinese attack on Taiwan, Admiral Rob Bauer, a former chair of the alliance’s Military Committee, told me. As of last January, when he retired from NATO leadership, Bauer was not aware of any concerted effort inside the alliance to prepare a strategy for this “worst-case scenario,” as he called it. “What are we going to do? Who’s getting which troops?” Bauer asked. “I think it would be wise to think that through.”Many military threats have seemed far-fetched until they happened. Before the Nazi invasion of the Soviet Union, in 1941, Joseph Stalin received repeated warnings from his own generals and spies. But he refused to believe them until the bombing started, hindering the ability of his forces to prepare. The U.S. likewise failed to prepare for the Japanese attack on Pearl Harbor. In the lead-up to the First World War, Europe split into two rival alliances, and no one predicted the scale of the destruction that their conflict would unleash.“The indications were clear that they would clash, and we just weren’t ready for it,” David Santoro, the president and CEO of the Pacific Forum, a research institute in Hawaii that focuses on Indo-Pacific security issues, told me. In 2023, Santoro and his team organized a round of theoretical war games, known as tabletop exercises, in which two American allies called for help at the same time: Taiwan came under attack from China while North Korea seized its chance to invade South Korea. “We were struggling to keep up and divide labor,” Santoro recalled. “And we weren’t even talking about Europe. I can only imagine what would happen if you threw Russia in there.”[From the June 2024 issue: The new propaganda war]A great variety of tabletop exercises happen all the time. Most involve two teams of military experts sitting around a conference table and responding to one another’s moves, like a multiplayer chess game. The organizers try to keep the rules simple and clearly defined. Such tight parameters do not reflect the chaos of warfare, but they prevent the games from getting too hectic when players from different fields of research talk past one another. This bias toward orderly games helps explain why so little research has been done on what experts call “multi-crisis environments.” Almost by definition, such scenarios would quickly get confusing.“It’s complicated, to be sure, but I don’t think it is too complicated to study,” Eric Heginbotham, an authority on war-gaming at MIT’s Security Studies Program, told me. “I just don’t believe that anyone has done it.” He cautioned that some secretive department within the Pentagon or elsewhere may have quietly analyzed this grim contingency and drawn up response plans.The general topic of a two-front war now gets discussed among military experts “more than it used to be,” he said. The Center for Strategic and International Studies, a think tank in Washington, D.C., published a lengthy report in June on the best ways for the U.S. to “counter an axis led by China and Russia.” But Heginbotham, who has worked closely with CSIS, said that none of the most prominent research institutes in the U.S. and Europe has organized war games on the subject. “You’d need two relatively big and elaborate games running simultaneously, with some sort of command authority setting priorities in the middle,” he said in an email. “Sounds very interesting.”In the public statements of senior NATO leaders, the risk of a multifront war has come up over the past year or so, though not very often. In December, a few months after Grynkewich issued his warning to U.S. allies, NATO Secretary General Mark Rutte mentioned the threat at the end of an interview that he gave to a German newspaper. “China is looking at Taiwan,” Rutte said. “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.”One of the most detailed analyses of this possibility, at least in the public domain, comes from an obscure research institute in Prague called the European Values Center for Security Policy. Its 35-year-old director, Jakub Janda, told me that he began studying the idea of a “dual-theater” war in Europe and Asia after the institute opened an outpost in Taipei, in January 2022. At the time, the risk of a coordinated attack from Russia and China seemed remote or, as Janda put it, “not a major consideration.”That began to change the following month, when Russian tanks rolled into Ukraine. Putin had visited Beijing less than three weeks before he ordered the invasion. He has since made at least four more visits to China, and another one is planned for November. Throughout this period, China has become the main supplier of technology to the Russian weapons industry while propping up the Russian economy through the purchase of oil and gas. Although they have no mutual-defense pact, Russia and China hold regular military drills to help keep their forces in sync.[Read: The autocrat’s dilemma]The first war game to simulate a joint attack from both of them took place at Janda’s institute in the spring of 2024. Finding experts with enough background knowledge to participate proved difficult for him. Most research institutions and think tanks have separate teams that specialize in their own regions, he said. “They work in their silos, with different expertise.”Over time, the participants grasped the way that wars in Asia and Europe could overlap and reinforce one another. The institute has already held roughly 20 rounds of war games on this topic, gathering experts in a variety of countries, including Japan and South Korea. The results have been particularly alarming, Janda said, for the Europeans. In almost every two-front scenario that he has studied, the U.S. prioritizes the Chinese threat and transfers military resources from Europe to Asia, leaving its NATO allies to defend themselves against Russia.In one hypothetical case, China begins the war slowly by banning the export of raw materials to Europe’s defense sector. It maintains the embargo for five months, long enough for European factories to run out of supplies and stop producing weapons. Then Russia, with full access to Chinese resources, invades a NATO ally in Eastern Europe.All of the scenarios in Janda’s series laid bare the need for Western unity. In the event of a Chinese attack on Taiwan, for example, the U.S. might demand that Europe impose severe sanctions on China’s economy, effectively cutting off trade. “But European governments don’t want to do that,” Janda said, describing how that premise played out among the experts. “The problem with European capitals is that Taiwan is far away. They want to focus on the threat from Russia, and that’s what scares me.”If Russia and China act in unison while the U.S. bickers with its allies, the chances of a Western victory in a two-front war begin to look bleak. The side that comes out on top, in other words, tends to be the one that moves with common purpose and remains united over time.