[dane-pgp]

You might not be able to wish away nuclear weapons, but if all countries in the world wanted there to be no nuclear weapons, they could (after solving climate change) introduce a global ban on nuclear energy and the possession of fissionable elements.

This would have to be accompanied by a powerful inspections regime, with big rewards for whistleblowers. Also, if a country did announce it had secretly produced nuclear weapons, or was discovered to have them, that would probably have to be treated as a casus belli, and all other countries would have a legal duty to launch a massive (conventional) bombardment of that country.

[Apocryphon]

The entire world was able to come together to ban CFCs, so there’s at least one precedence of a harmful substance getting universal prohibition. And there are all sorts of human rights conventions on what may or may not be used in war.