We must try to break the symmetry of the game.
There are the non-imperial civilizations, those of a tribal style.
Celts, Germans, Iberians...
Then there are those whose destiny is to conquer nations and bring civilization to others.
There are others that seek to be in the middle, like certain Greek cities.
Honestly, the game should change its gameplay according to the culture.
There are some who want to live in the land of their ancestors, the land of their gods, to be free, and others who will seek to enslave everyone and demonstrate that their tribe and nation was the one that would bring order to others.