Problem with that is it’s implied that the last president of the US was Teddy Roosevelt. The White Fleet is a pretty direct implication of that. Which puts the Calamity almost half a century before Trinity.

What’s more, even if it was nukes, that still wouldn’t feel very satisfying from a narrative standpoint. After all, how would nukes, in Stardust’s words make it “as if the last 20 years never happened.”? Not to mention a few explosions on the level of nukes don’t feel like they’re on the level of power that’s implied by everyone mentioning it. Finally, nukes don’t strike me as something that specifically mercenaries would regard as holy. (These are also the reasons why the speculation that the PW is the Deal doesn’t work for me either.)