I want to read an alt-history from the Fermi-verse where the first bomb at the Trinity test was powerful enough to cause a cascading fusion reaction throughout the Earth's atmosphere, allowing only 1940s-era submariners, hard-rock miners, and sea life to repopulate the surface of the planet.

https://blogs.scientificamerican.com/cross-check/bethe-teller-trinity-and-the-end-of-earth/