Problem: AI not upgrading units. Reason: Some upgrades require resources, which aren't needed for original unit. Solution 1: Encourage AI resource trade to be willing to buy them more and sometimes temporary trade away their only resource. Pros: More active resource trade, involving human player too. Cons: A lot of tweaks needed and potential exploits arise. Solution 2: Give AI a cheat to be able to upgrade units without resources for additional gold, but willing to buy the resource anyway. Pros: Easy to implement. Cons: It's a cheat visible to players. Solution 3: Let AI build less such units and make AI dismiss them if no upgrades expected and better units are available. Pros: Most natural behavior. Cons: Requires a lot of efforts to implement. Problem: City-states spawn units. Reason: City-states with late speciality districts or with full district have nothing else to build. Solution: Let city-states build other districts. Focus more on projects once they have them. Problem: AI not offensive enough to threat winning conquest. Reason: Restraints to conquest through warmonger penalties. Solution: AIs should be less angry over other AI warmongering on higher difficulty levels, and should ignore those penalties more.