Once upon a time, when the airplane and the bomb were both new technologies, people looked into using them to make war "humane." And in a 1928 issue of Popular Mechanics, writers speculated about what that would mean.
Would you like to live in a world where you could just wake up and belong to another nation? I don't mean figuratively. Popular Mechanics explains:
A thousand airplanes, each carrying five pounds of chloroform, could put the inhabitants of cities as large as Chicago or New York to sleep in a few moments - and similarly, planes flying above trenches might induce peaceful slumber in whole battalions of soldiers. They could be awakened having suffered relatively little harm.
Alternately, they could be either puzzled by the faint smell of chloroform being carried away on the wind, or die like butterflies in a killing jar. Those who awakened might still be inclined to fight - especially in cities like Chicago and New York. Chloroform was used as an early anesthesia, but it was abandoned as soon as alternate methods were found. People who had just a bit too much went into heart and respiratory failure as the drug depressed their nervous system. Soon chloroform was used almost exclusively to kill insects for collections and to kidnap ladies in 1930s movies.
The idea of the chloroform bomb was revived, lately, in a booklet sponsored by Al Qaeda, but it was meant a localized way to do damage, not a form of "peaceful" warfare that could subdue cities. So it looks like we'll be able to sleep soundly knowing that enemy soldiers aren't taking selfies next to our unconscious bodies for a bit longer.