When humans went to war in the past, they created weapons that can kill their enemies quickly and painlessly. As such they banned weapons and ammunition like hollow point bullets, flamethrowers, and any weapons that don’t kill humans as quickly as possible. -- Anon Guest
They say war never changes. They lie. What actually never changes is the depths to which combatants will sink to in order to gain a victory -any kind of victory- over the other side. Germ warfare is as old as the ability to fling a corpse over some fortified walls, or to leave one upstream of the besieged city's water supply. Murdering the innocent and unarmed is even older than that.
In war, more civilians die than any number of soldiers. They remain uncounted because they are civilians. They aren't important to the movers and shakers who create the wars in the first place. In war, there are terms of combat and the main battle is in seeing which side decides to ignore those first. Or which side can create a supremely vile weapon which wasn't discussed in the original terms of combat. New and more disgusting or horrifying ways to end the opposing forces.
First, of course, was germ warfare. Predating even the germ theory of disease dispersal. Next, came an assortment of attacks on supply chains. Burning the fields, diverting the water, or addicting the populace to debilitating drugs. Following that came mass poison. Adulterating the water supply has always been popular, but when they discovered how to adulterate the air. Gas attacks became the new terror. From there, things could only escalate.