you could add a prerequisite tech that can only be researched via a focus/decision

this tech would be required to research nuke tech, then just add the decision to unlock it to the nations you want

is there a mod for this? i doubt it, but you can make it, it's not that hard i've been told

the AI doesn't really make nukes very often outside of the major players anyhow even then it's rare to see them used, i don't think i've ever seen the afghan AI research, let alone make, nukes, despite it being possible

It really should be harder to actually research nukes in general, but a hard rule would probably include the worst offenders (Nazi Germany in particular, a nation which murdered every nuclear scientist in its borders) anyways, and would still lump every country into it onto more or less the same playing field. You'd need way more depth to it to actually get something more realistic than what's already there.

Not like it really matters one way or the other, though, since they're mostly just a way to make late-game fights move faster and not an actual useful research.

All that aside, I think you can just specifically disable dropping nukes by national focus. I know you can enable it through that because Millenium Dawn did last time I played it, so I'd assume the inverse is true as well. It might also be possible to make being a certain country a condition to research a tech. Worst come to worst, there's both adding a prerequisite as Big [REDACTED] Marty mentioned or just moving the nuclear tech tree to its own category and making that category country-specific.

Germany was the only other nation on earth which had anything resembling a nuclear project at the end of WW2? Heisenberg had managed to build a small scale reactor. But he wasn’t close to creating a bomb

Originally posted by ConsiderableFlux:

Germany was the only other nation on earth which had anything resembling a nuclear project at the end of WW2? Heisenberg had managed to build a small scale reactor. But he wasn’t close to creating a bomb

https://en.wikipedia.org/wiki/German_nuclear_program_during_World_War_II

"The scholarly consensus is that it failed to achieve [a nuclear reactor which could run long enough to completely separate nuclear isotopes], and that despite fears at the time, the Germans had never been close to producing nuclear weapons."

Meanwhile, British efforts within the Manhattan Project continued to the end of the war following the end of their own, individual project ( https://en.wikipedia.org/wiki/Tube_Alloys ), and even the Soviet Union had the political will to kickstart their program, albeit not much more in the way of actual progress and a much later start ( https://en.wikipedia.org/wiki/Soviet_atomic_bomb_project ).

The Nazis just didn't have the means to build nuclear weapons. They dropped the country's best scientists into Auschwitz and declared half the field to be "too Jewish" to be taught in universities. And that suppression and eradication of so-called "degeneracy" is a core part of fascism as an ideology. The only change that would have allowed Nazi Germany to successfully build nuclear weapons was to stop being Nazi Germany.

I'd say overall it depends on how much industrial development the country in question has; it is logical that anybody with enough productivity can; but the problems are the investments needed to be made to be able.