War is strange.
In the thick of it, all purpose is lost, and meaning ceases to exist.
One loses sight of time, and in the fields drenched in red, with that metallic stench being the only constant, the world itself is drains of every other color.
Cain had come to terms a long time ago that having to turn his blade towards other humans was a guarantee.
This acceptance stemmed from conflict of interest, as well as the strange fate the Celestials push onto the worlds their remnants fall upon.
Most Celestials were constantly in conflict for new territory. Even upon their death, the more territory a Celestial possesses, the greater the reserves of Divinity they can draw upon for their rebirth.
This amount of Divinity is directly related to the probability of the rebirth being success and stable.
And because Celestials that were still alive still lusted over more territory and more divinity shackled, it made sense that they would want to hurry up their expansion.