Wouldn't it sound better if you said "we gave it back to the natives" or something?

That gas was produced way back in WW1 but the army didn't get any chance of actually using it.
The use of the gas was a response to the Ethiopian warriors using Dum-Dum bullets on both military and Red Cross personnel, and after they mutilated and castrated some Eritrean and Italian squads they had captured.
Furthermore, the Ethiopian emperor, Haile Selassie had ordered every single fighting capable person to fight to the death for the country, in a method that would make the Japanese seem tame in comparison. Selassie only excluded the elderly, crippled and pregnant women from fighting, and of course he wasn't sharing the burden, since he escaped to Jerusalem after losing the capital and immediately asked for the help of the British. I'm not saying that the use of those weapons was justified, but Selassie would have sacrificed the life every single person in his country before surrendering.

I think this wasn't fair, like America using nukes, but war is never fair.