How does the Talmud interact with modern war?

Please tell me if this needs to go in a separate thread. I’m not trying to talk about politics or antisemitism, but mainly trying to figure out how to approach something I’ve been struggling with theologically. Again please do not reference any ongoing conflict, I’m looking for a purely theological answers here.

Let’s start off with a hot-button issue, but it allows me to ask a few questions.

How do we, as a faith, legitimize nuclear weapons?
– How does Judaism engage with proportionality (a weapon that can kill en-masse and military/civilians) when the Talmud echoes a punishment matching the crime?
– Along that same line, are there exceptions to the laws for when the Jewish people and nation are under threat?