What war did chemical warfare start to come into focus?

I have to do a project about weapons, and i would like to know about what war did chemical warfare start to be an idea. I know that it's banned now, but i think it would be interesting to include this in my project.|||ww1 they started to us mustard gas and it was a serious problem killing many soldiers until gas masks were given to troops, and the iran iraq war saw widespread use of chemical warfare..... so we invaded a country with chemical weapons not technically weapons of mass destruction but still deadly|||If you go way back, the Romans used salt to poison the land that used to be Carthage so crops would never grow again.





Before that, often poison was used on some weapons and poison was used to pollute water sources that enemies might use.





The Spartans would ignite pitch to cause toxic fumes against the Pelopenisians.





When the Turks invaded Europe, the defenders of Belgrade used cloth dipped in chemicals to create toxic fumes.





During the US Civil War, the use of poison as a weapon was specifically outlawed, so you kind of have your first ban on chemical weapons.





If you want to look at biological weapons, diseased corpses would be flung over the walls of castles or cities.





WWI was the first large scale, organized use of chemical weapons though.|||1|||World War I|||WWI