You might find this an interesting read: https://acoup.blog/2020/03/20/collections-why-dont-we-use-chemical-weapons-anymore/ https://acoup.blog/2020/03/20/coll

You might find this an interesting read: https://acoup.blog/2020/03/20/collections-why-dont-we-use-chemical-weapons-anymore/ https://acoup.blog/2020/03/20/collections-why-dont-we-use-ch... TL;DR is that it's not used these days because it wasn't actually all that effective, at least not when used in modern warfare. That is also why it's (mostly) honored, even though many other prohibitions under international treaties are ignored by the largest (ab)users. However, if conditions similar to WW1 become dominant on the battlefields - and, looking at Ukraine, trench warfare at least is back in some way - this might get re-assessed.