At the moment, we have a fixed borders mechanism whereby I can claim a tile on which I've placed a unit. I'd like to expand this concept: I'd like to see the ability to arbitrarily draw one's desired borders. Then we could have regions which are claimed by two (or more) Civs, and this would lead to diplomatic tensions. You might need new associated diplomacy options. If you make a wild claim for land which is very far from your city and near to someone else's, you probably won't be taken seriously (Spratleys?). The other Civ could claim the land themselves and if they're close enough to use it they could. You could protest diplomatically, send military units, or relinquish your claim. Would add a whole new dimension to the game. If that's too ambitious, perhaps we just make it such that removing your unit from a claimed tile doesn't relinquish the claim. Would need to teach the AI to claim land appropriately I guess.