What I want to know is if if territories will be associated with geographical regions, or if they are randomly made. (Think rivers and mountains define borders for the first, and the post-WWI borders that still trouble Africa and the middle east today). Are the regions limited to one city? Are other factions able to build a city in that territory or region and cause conflict or cooperation based on Culture? If it is forced to one city, then its static and easy to manage. If other cities can be settled in that region from other cultures/factions then it becomes dynamic, which is more elaborate but more realistic.
I like the Endless legends large territories for easier management of areas, but Civilizations is more immersive to me.
In a mix of the two, a faction would have an influence over a region and the more influence the more control over people and resources from that region. While other civilizations can settle or grow their territories (like in Civilization) into that region causing power struggles over resources. But if that region is foreign (like Egyptians in Norway), then they get negatives on them. It also hinders empires from just taking everything around them. Their influence will be too foreign or savage to the natives thus causing it to be weaker in farther away regions and recently conquered regions.
I think Influence is a major part of territories as well. You can't control where people go, and so you receive people from other places, maybe unsettled wild-land nomads in the earlier start, but large amounts trade bringing in people from around the globe talking highly of their home in the later game.
Are there similarities between the mountain people and the plains people for them to work together? Maybe they may be too different, and the mountain people don't accept the ways of others in your empire and so it becomes more difficult to expand in that region. All these would have an effect of how easy it is for your empire to grow. Do the surroundings like you and want to be part of you? Or do they resist you like the Gauls with Rome?
I see total war games as static as they are unmoving territories, but are restricted by the fact that reference existing places, they don't create new maps like Civilization does, even in their Total War: Warhammer games they stick to what was already built. I think their games make a good reference with public order and religious/cultural influence, but I don't think much else be applied to Songs of Eons d/t that SoE's philosophy is much closer to Civilizations style.
In summary I like the static Territories for geographical reasons and managing simpler areas with multiple mechanics. Like city builders, or Total War games, Endless Legends. But I prefer dynamic for territories and constantly changing worlds with influence and expansion mechanics, like Civilization games, Endless Space.