On a side note, World War II was not entirely free of chemical or biological weapons, at least in China. Of course, the Japanese never dared use them against America, for the same reason Germany didn't use them--the fear of deterrence. Vast stockpiles of chemical weapons did exist for this purpose (iirc, a ship containing such chemical weapons blew up in an Italian port in 43 or 44 and poisoned many).
And it's because of deterrence that Vietnam didn't go nuclear--and Korea for that matter, despite serious contemplation of the option and significant infighting over the matter at the highest levels of command. If not for the fear of retaliation, governments tend to use whatever means seem relevant to the goal they've set out to achieve. In World War II's case, the Casablanca conference settled this as the unconditional surrender of the Axis powers--tall order.
And Operation Downfall, the planned invasion of the Japanese home islands, most definitely would have involved the major use of chemical weapons. We didn't want another Iwo Jima. (Then again, what's the difference, we'd already killed and "dehoused" millions with conventional bombing anyway.)
Of course, the greatest examples are the nuclear bombings. In the only major war a nuclear power has ever fought against a nation without nuclear weapons of its own or allies possessed of such weapons, the nuclear power used its nuclear weapons with little hesitation. Food for thought.
The inference seems to be that the fear of retaliation keeps the Romulans from imploding Vulcan. In the prime universe, anyway.