Peace is the absence of war.
The PA and EotH can build up their forces, and then their aggression level rises by the later eras.
I know this is utterly impractical from a gameplay standpoint for many reasons, but, is it possible from a programming standpoint to have a relatively bug-free gameplay mechanic where a truce is suggested and the opposing faction's aggression level drops? (if you attack any of their territory their aggression level rises, and it would be wise to suggest a truce when an attacking force isn't transiting between systems. Withdraw your forces from their territory before suggesting the truce).
I'm sure such a system doesn't work, but I am intrigued as to how. Apologies if this has been suggested before.