At the height of the summer, the mood was optimistic in the world’s financial capitals. Powered by the AI revolution, the US stock market had rallied to a fresh all-time high, as investors bet the multitrillion-dollar investment spree would overshadow the hit from the Iran war.

Now the warning lights are flashing red. As the fighting in the Middle East intensifies without clear sign of a resolution, financial markets have been thrown into renewed turmoil. A slowdown looms in the AI arms race, and tinderbox conditions in the market for government debt are fuelling alarm.