I was wondering about the state of the deterrence in place against nuclear weapons usage, having always assumed it to be massive, and I can't tell if there's actually any formal international treaty about the use of nuclear weapons in war.
https://en.wikipedia.org/wiki/List_of_weapons_of_mass_destruction_treaties has arms-reduction, non-proliferation, and test ban treaties, but apparently nothing about who you actually nuke. I think Geneva says you can't target civilians with any weapon, but does anything prohibit nuking your enemy's army?
If things escalate to the point where nuclear weapons get used, that probably implies enough of a breakdown of order that it doesn't matter what any treaty says.
India vs. Pakistan: the nuclear option is dangerously close, and nobody seems to want to prevent it
http://qz.com/541502/a-nuclear-war-between-india-and-pakistan-is-a-very-real-possibility/