The list of chemical weapons uses in the last century is nice. I'll point out though where it suffers from 'mainstream' bias. That chemical gas usage in Iraq in 1920 is omitted is acceptable, the claim can be disputed with reason. A similar claim about use of chemical weapons by the Syrian is taken as fact because everyone says so, while it's very doubtful that the Syrian army has resorted to chemical weapons. The very significant fact that Iran always refused to even make chemical weapons let alone use them while Iraq used them abundantly is turned into them running a weapons program after some restraint. They never made the weapons. Sure, proponents did some research, but proposals for weaponization were met with an unequivocal no from Khomeini.
I wonder about the claim that chemical weapons killed millions of people . How many besides the german concentration camps? Often war casualties were not killed but maimed.