DBWI: No Large Scale Chemical Warfare Post WWI

Is there any way we can avoid the large scale use of chemical warfare after the First World War? Particularly in the Anti City Strategic Bombing Role?

Mihnor Colonial conflicts are allowed, near ASB to keep it from being used there
 
A Much longer First World War would likely. Maybe if White Peace hadn't been signed in 1916, The Horrors of Chemical Warfare would of been been felt more heavily. However, by time the Second World War, it was already so heavily integrated into Standard Doctrine of the Various Armies of the world.
 
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