This may be an existential question, but why, indeed, do people go to war?
One reason people and nations go to war is to settle a dispute that they are unable to resolve peacefully. The stubbornness exhibited in this case is often based on a lie that is perpetuated and repeated so much that even the party that is lying often starts believing it.
This is particularly the case in the case of an internal or civil war.
People go to war because they lie to themselves that everyone believes their lies, only to be confronted by an opposition that feels the exact opposite.
While war often happens when both parties are lying to themselves and others, often it takes one side’s lie for a war to break.