Pandemic, economic depression, riots. One more thing happens and we might be in real trouble, and if you think no new thing could go wrong you've not been paying attention.
My guess, honestly, is something like a coronal mass ejection. It'd be a bit worse for character if it only impacted half the country (which is possible), but who knows what result would actually be worse. Particularly now, with international trade minimal, how would infrastructure get rebuilt?
Hurricane season is about to begin, right? How likely is it that nothing major happens – worse than a coin flip, I think.
They say the San Andreas fault is due for a big one. Aren't volcanic eruptions and Yellowstone-related disasters something that can be predicted? Does that mean it's an extremely minor risk – until the sensors go off? Because if we had ten years warning about Yellowstone right now, we'd use the first year doing nothing, for sure.
Drought, heat wave, floods, those all seem like they might be in season.
China is gearing up for war with India and Taiwan – and America is obligated to help Taiwan defend itself, so World War 3 isn't out of the question.
It's not like we're any safer from terrorism. Bio-terror is horrifying, but even bio-error seems more likely than ever, but in truth it's just that the risk has been steadily climbing for a long time, not that there's been any sudden jump.
I have no idea what will happen. Or where in the world it might happen. But when everyone is retreating to their home country, and ties between us are weakest, I know it will hurt the most.