This kind of cynicism is a strange thing. It sounds like a hardened realist talking, but in reality it's fairly naive.

Chemical, biological weapons use has been greatly curtailed by rules of war. So has "aggressive" war (war, because we want your territory). So have various civilian targeting tactics. They haven't been eliminated, but there is a lot less than otherwise. It's not perfect. Enforcement is erratic and case-by-case. Powerful countries are more exempt than weak ones.

Nuclear proliferation has been effectively slowed by the NPT. Again, not perfectly but better than nothing.