At the height of the summer, an unmistakable wave of optimism pervaded the world’s financial capitals. Fueled by the relentless momentum of the artificial intelligence revolution, the US stock market had rallied to a fresh all-time high. Investors eagerly bet that a multitrillion-dollar investment spree in cutting-edge technology would easily eclipse and absorb any economic shock stemming from the widening war involving Iran.
Now, just weeks later, the warning lights across global financial systems are flashing red. As fighting in the Middle East intensifies without any clear sign of a diplomatic resolution, global markets have been thrown into renewed turmoil. At the same time, a looming slowdown in the ferocious AI arms race and increasingly volatile conditions within the market for government debt are compounding alarm among economists, traders, and central bankers alike.
Over the past week, the US government’s borrowing costs climbed to their highest level since 2007, triggering severe knock-on consequences for the finances of households, businesses, and foreign governments worldwide. Underlying this surge is a pervasive fear that Donald Trump’s war is stoking higher levels of structural inflation. Compounding the anxiety are the president’s aggressive tax and spending plans, which have driven Washington’s national debt levels above the staggering milestone of $40 trillion, leaving investors deeply rattled about fiscal sustainability.
As global oil prices surge past $100 a barrel, sparking heavy selling pressure across the sovereign bond market, seasoned financial observers are asking an ominous question: could shares be the next in line for a catastrophic crash?
With the benchmark S&P 500 index of leading US companies currently sitting roughly 3% below its all-time peak, and a combined market valuation of more than $20 trillion concentrated in the "magnificent seven" tech titans—Nvidia, Apple, Google, Microsoft, Meta, Amazon, and Tesla—concerns are mounting that equity markets are dangerously overextended just as severe economic storm clouds gather.
"These are febrile times," wrote Albert Edwards, a senior analyst at the French investment bank Société Générale, in a note to clients. "The key worry for investors and policymakers alike is the extent to which the current oil price ‘shock’ will ripple through the global economy and whether it will necessitate sharply higher, recession-inducing, interest rates."
Famed for his characteristically gloomy predictions, Edwards believes the classic ingredients for a full-scale financial crisis are quietly assembling amid the tinderbox conditions of the US government debt market.
So profound is the anxiety that the ongoing conflict in the Middle East will entrench inflation that the US Federal Reserve openly defied political pressure from President Trump this week, executing its first interest rate hike since 2023. As households and businesses come under mounting pressure from spiraling energy bills and surging fuel prices, central banks around the world are following suit with their own tightening measures.
Financial market pricing now suggests the Bank of England will raise interest rates four times before the end of next year, even after choosing to keep borrowing costs on hold this week. Meanwhile, the European Central Bank implemented a rate hike last week, highlighting the direct economic toll the escalating conflict is exacting on the eurozone, and the Bank of Japan pushed its policy rate to a 31-year-old high.
The rationale behind these central bank actions is clear: by deliberately increasing the cost of borrowing, policymakers hope to cool economic activity and prevent short-term energy inflation from becoming permanent. However, this medicine will inevitably hit households and businesses that are already struggling through a protracted cost-of-living crisis. Rising unemployment is widely expected to follow, compounding the fiscal challenges facing governments already swimming in massive mountains of debt.
Historically, a US recession has followed roughly three to three and a half years after a central bank’s initial interest rate hike, according to calculations by Deutsche Bank’s Jim Reid. Financial markets have a well-documented habit of falling—or even violently crashing—before an economic recession officially begins, often mounting a recovery only after the broader economy has plumbed its depths.
Yet, the primary dread haunting institutional investors is that the ultimate safety net of the modern economy—artificial intelligence—could turn out to be a hollow promise, having instead inflated a colossal speculative bubble within the US stock market.
One of the most popular valuation metrics used by investors to gauge whether an equity market is overvalued is the CAPE ratio, or cyclically adjusted price-to-earnings ratio. This metric has now climbed to its highest level since the turn of the millennium, indicating that American equities are exceptionally expensive relative to their actual corporate profits.
The CAPE ratio for the S&P 500 share index currently stands at nearly 41 points, which is more than double its long-term historical average of roughly 17 points. This puts the market dangerously close to its all-time record high of 44.19 points, recorded in December 1999 right on the eve of the infamous dotcom crash.
Underscoring the sheer magnitude of the challenge, independent research from Fathom Consulting demonstrates that for the multitrillion-dollar AI boom to eventually turn a genuine profit, AI-related sales across the participating technology companies would need to skyrocket by between $600 billion and $800 billion within the next two years.
Against a deeply nervous backdrop where investor patience is visibly wearing thin, Fathom Consulting assigns a 30% probability that the AI bubble could burst as early as next year.
Brian Davidson, an economist at the consultancy, explained the fundamental disconnect: "For all the impressive advances in AI technologies in recent years, the economics behind the current capex boom do not work. Yes, recent AI advances could yet unlock huge productivity gains; but sales of AI models need to increase by hundreds of billions of dollars per year over the next two years to justify the current spend. Such growth appears unlikely."
Investors are clearly taking notice. More than 1,000 financial professionals registered for an emergency analyst call conducted by Jefferies this week, titled "AI Extinction Warnings," following public appeals from top tech executives urging a slowdown in what they termed "reckless" AI development.
The current situation bears striking parallels to the dotcom crash of 2000, when numerous internet startups billed as revolutionary technologies dramatically collapsed in value. It serves as a stark historical reminder that even when a technology genuinely changes the world, investors can still lose their entire fortunes if they finance too much infrastructure long before genuine consumer and enterprise demand materializes.
"It took a decade or more for demand to catch up with the infrastructure laid down in the British canal and railway and US telecoms and fibre booms—and many investors never recovered their capital," points out Adrian Cox of the Deutsche Bank research team.
Sobering comparisons are also being drawn with the buildup to the Great Crash of 1929. A century ago, droves of small US investors engaged in buying stocks "on margin"—acquiring high-risk equities using borrowed money—only to be utterly wiped out when the market collapsed, triggering the Great Depression.
A modern echo of this phenomenon occurred this year in South Korea, where an army of retail traders aggressively bought shares in AI-linked chipmakers using heavy margin loans, briefly doubling the value of the blue-chip Kospi index. However, once the broader market turned downward, these traders were battered by a massive wave of margin calls, forcing brokers to demand immediate cash injections. With many unable to pay, forced liquidations ensued. According to data from Goldman Sachs, 1.2 million South Korean retail investors were hit by margin calls—roughly the equivalent of one in every thirty adults receiving an alarming call from their broker demanding urgent funds.
The gargantuan spending plans announced by AI infrastructure companies are simultaneously stoking fears that the corporate sector is simply borrowing too much.
One prominent firm caught in this dynamic is Oracle, the major database software vendor. Oracle shares surged high a year ago following the announcement of a major cloud computing partnership with OpenAI, the creator of ChatGPT. However, those gains have since been cut in half as investors increasingly fret that the company may have taken on excessive debt to finance the construction of massive new data centers.
Additional signs of stress are clearly visible across wider credit markets. The Bank of England reported this summer that the yield spread between the riskiest corporate debt and the safest high-yielding bonds has widened significantly since the outbreak of the war in Iran, demonstrating a profound reluctance among investors to hold high-risk debt instruments.
As government bonds experience a sustained sell-off, falling prices have driven up sovereign debt yields. These higher bond yields inherently make equities less attractive to institutional portfolios, as investors have less incentive to buy riskier stocks when safe government bonds offer compelling guaranteed returns.
In the United States this week, this dynamic manifested as the yield on benchmark 10-year Treasury bonds crossed the psychologically crucial threshold of 5%.
This level is "seen by some as a threshold above which financial markets might go into meltdown," noted John Higgins, the chief economic adviser at Capital Economics. "While we aren’t convinced that 5% is that ‘magic’ number, higher Treasury yields would certainly pose a risk to the sustainability of the US public finances as well as threaten equities," Higgins told clients.
Bloomberg macro strategist Simon White argues that systemic trouble would truly accelerate if the US 10-year Treasury yield were to climb past 5.25%. He calculates that this represents the critical inflection point where, historically, stocks and bonds begin to compound losses in one another.
Despite the pervasive market turbulence, pockets of cautious optimism remain that a full-scale financial crash can still be avoided, driven partly by hopes that markets are overestimating the ultimate inflation risks posed by the Middle East conflict.
"A major downturn would need a trigger. Further geopolitical instability could be the catalyst, but we’ve long argued that the impact of geopolitical shocks on economic activity is overstated," analysts at Oxford Economics wrote in a note to clients. "Resurgent inflation and policy rate hikes by the Fed and other central banks are another candidate. However, our view on inflation is less alarmist—we think market expectations overstate the risk of further policy tightening."
For many investors, a cooling-off period in feverish AI capital expenditure could act as a vital safety valve against the creation of a catastrophic bubble.
Crucially, there are tangible signs that artificial intelligence is finally beginning to translate into genuine economic growth. The US economy has recorded a notable uptick in productivity growth, while AI is also cited as a primary driver behind the UK economy defying gloomy forecasts to deliver surprise growth, becoming the fastest-growing economy in the G7 during the first half of the year.
Such a turnaround in national productivity could eventually help corporations with sky-high share prices justify their lofty market valuations. Nevertheless, it remains an exceptionally high-stakes gamble during a period of intense and unpredictable global volatility.
"Do I think there’s a significant dose of reality though in that productivity miracle in AI? Yes," Andy Haldane, the former Bank of England chief economist, told LBC this week. However, he warned that the broader financial architecture remains fragile.
"I don’t think outright collapse in a dotcom bubble type fashion. But could I see a slow release of air that doesn’t collapse the world economy, but slows it down? Yes, I could."
