The gas bombs were fired from Steel Behemoths which were made by the Fabrication Machine under the orders of Chancellor Ferdinand for his Nation's military. When the Machines turned on The Nation's military, it used this toxic gases to kill everything and end the human race.
The gas bombs consist a noxious chemical composition of poisonous gases such as chlorine gas and propane gas. This form of weaponry is powerful enough to virtually exterminate all organic matter of any form, shape, size, and tolerant level of resilience within the earth’s troposphere.
During the final days of the Machine War within the Nation, a scene is shown where three gas bombs are fired by three Steel Behemoths. As soon as one of the bombs lands on the ground, the toxic fumes inside the tank of the gas bomb are released, which resulted in elimination of several flowers by its vicinity.
When 5 was running away, he is hit on the back of his head with one of the bombs, experiencing a temporary concussion and losing his left eye.
The gas bombs played a key role in not only killing off the human race but also killing every other organic lifeform such as plants and animals, leaving the Earth a dry and barren wasteland devoid of any kind of life.
Trivia[]
- It is uncertain whether or not the Chancellor ordered the creation of these gas bombs, given such weapons were missing in the flashback of the Steel Behemoths creation. It's doubtful that the Chancellor would want all of humanity (let alone plants and animals) to be extinguished because it would contradict his ambitions of establishing a planetary empire. This adds further clarity that the gas bombs were created by the Fabrication Machine in its genocidal crusade against all organic life on Earth.
- Withal evidence of how effective the gas bombs were at wiping out life and externalizing extensional noxious chemical subsistence can be noticed by the corpse of The Scientist in regard to how his deceased body barely evinces any visual signs of biotic corruption or putrescence despite a prolonged time period after the cessation of the Machine War.
- It is possible that the gas bombs were capable of killing natural microorganisms higher up in the atmosphere, as propane/mustard gas fumes are able to travel a certain altitude in the air and still have a noxious effect.
- It is heavily implied by the ending that the dead stitchpunks' soul fragments being released and merging into a unified quantum of ethos in the sky caused a supernatural rainfall that not only dispelled the toxic residue still lingering in the Earth's atmosphere but also brought life back to Earth.