(emphasis added)Although one of the Powers in conflict may not be a party to the present Convention, the Powers who are parties thereto shall remain bound by it in their mutual relations. They shall furthermore be bound by the Convention in relation to the said Power, if the latter accepts and applies the provisions thereof.
Obviously, they haven't done so.
To your second post, I agree and I never really disagreed with that part - I was just noting that the nature of this kind of war was never really considered. But since they (and therefore, we) aren't bound by it anyway, the rest doesn't matter.