There’s a “slight” difference between tear gas and chemical weapons. Ones cause temporary (but very strong) inconvenience (of course there maybe some one off complications), others are designed to kill you, as efficiently as possible.
The biggest difference is political: when someone the media doesn't like does it, it's a chemical weapon. When someone the media likes does it, it's nothing.
It's disingenuous to pretend that the chemical weapons of the WW's and the massive cold war stockpiles of VX or sarin are in the same class as deliberately nonlethal lachrymator agents used in riot control. The fact that chemical weapons treaties technically ban pepper spray in the same manner as nerve gas doesn't mean it's a massive evil of police overreach -- there's plenty of low-hanging fruit on that topic without needing to make ridiculous arguments.
GP isn't wrong though. Tear gas of the type used by civilian police forces against the general population is illegal to use in war. It is a war crime to use it.
Tear gas was developed by France and used on the battle field in WWI before being used for "crowd control".
"Riot control agents, including tear gas and other gases which have debilitating but non-permanent effects as a means of warfare, is prohibited in armed conflict under the 1993 Chemical Weapons Convention."
And, if a government's leaders feel they need to gas, assault with sound cannons / water cannons / pepper spray, use flash bang grenades, beat with clubs, and/or fire rubber coated steel bullets at their population, it might be taken as a hint that the government involved has lost the consent of the governed.
This is one of those sayings that's technically true but misses the point by a mile.
A wounded soldier is a greater burden than a dead soldier, so a possible tactic would be to deliberately wound. Some people thought that was especially amoral, so they added a rule against it to what they called international law.
So most police weaponry is illegal under international law, but it's illegal because it's less deadly than the permitted alternative.
> Now, I want to leave aside, for the purpose of this essay, the use of lethal chemical agents in genocide, the use of non-lethal chemical agents entirely, as well as the use of things like defoliants that were not intended to cause casualties (even if they did). Those things are all important, but if we get into talking about them, we will never get anywhere. Instead, we’re focusing on the battlefield use of lethal chemical agents against either opposing combatants or civilian populations.
Obviously different laws apply to different groups. The police can also do things (arrest people) that would usually be a crime for soldiers to do. Tear gas use by police is either right or wrong, useful or not useful, justifiable or not justifiable, but it's not really related to why chemical warfare is banned in war. We also don't justify the ability and legality of police to kill based on the legality of killing enemy combatants in war, either.
We can compare them and see that the police force oversteps its civilian role. Your point about the requirements to kill enemy combatants strenghtens that arguement.
My point is that we don't define what police do based on what soldiers do, so it's a red herring in terms of politics and legalities. We define whatever the limits on policing are separately, and tear gas is specially carved out for use by the police. My point isn't that that's right but that it's again not defined by the reasoning used to prevent escalatory chemical warfare in an actual war.