Iran is the exception that confirms the rule. They were so heavily sanctioned that it became feasible for them to say "screw it, we will do nukes anyway". I won

Iran is the exception that confirms the rule. They were so heavily sanctioned that it became feasible for them to say "screw it, we will do nukes anyway". I won't say that nuclear proliferation is completely stopped, but the system works for the most part. China and Russia are old nuclear powers and them having nukes is expected. Better counter examples are India and Pakistan, but I don't know the history of their nuclear programs well enough to comment with confidence. The chemical weapons in Syria were old stockpiles and I'd argue that the use there was not an increase of their use, but an opportunity attack. I don't think that there are many groups who currently have any kind of chemical program and can use it systematically.