Early yesterday morning, Donald Trump issued a threat on his social media platform Truth Social that would have sounded implausibly extreme if a comic book writer had put it in the speech bubble of a mad scientist or costumed supervillain. “A whole civilization will die tonight,” the president wrote, “never to be brought back again. I don’t want that to happen, but it probably will.”

Taken seriously, this sounded like a threat to use nuclear weapons. At bare minimum, Trump was underlining his earlier pledge to destroy the infrastructure underlying the day-to-day lives of ninety million Iranian civilians by systematically destroying the country’s bridges and power plants. Iran has shown that it retains a considerable supply of missiles and drones, as well as the continued loyalty of allied forces around the region like Hezbollah in Iran and the Houthi government in Yemen. If any version of Trump’s threat had actually been carried out, Iran surely would have done everything in its power to inflict comparable levels of damage on Israel and the Gulf monarchies (which host American military bases). It’s hard to imagine the global economic chaos, never mind the spiraling waves of death and suffering, that would have resulted from anything like this scenario playing out.

As of yesterday afternoon though, it looked like that was exactly what was going to happen. Then Trump backed down. In doing so, he showed something that it’s going to be important to remember next time hawks tell us some new war is going to be an easy victory: even global military and economic juggernauts have their limits.