Wow, "weak countryside, strong core"this is the kind of mechanics I always wanted to see in age of empire or in any RTS actually. Nice to see im not the only one.In think it would be more coherent if all building that can be build in the neutral zone would cast at least a small territory. There would be a line for the national border, and another for the city-limits(that could appear only when you want to construct a building that as to be built within a city limits)
So that way, you’ll have to build an Outpost or Dock that cast territory before you build a Storehouses and Farmsteads. Maybe you could also build wooden walls and wooden defences to protect those small outposts.
it would go into the direction of
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Outpost settlement - weak settlement for gathering ressources, conquer new shores or to take strategic point on the map
City settlement - Strong settlement to expand dramatically territory, enable trading, build more buildings, armies and better defences
SMALL DESIGN THOUGHT - I definitely think that civic center should look more like a camp at first and grows up as a real city center as the city changes phase. It would be the same for new City settlements. Something like that image (i like the idea around the well)