The Cities:



They are often either left with only the militia or a single unit. They are often not upgraded with defensive structures. This can be easily fixed if you double the militia units in a city and add ranged units as well. It will give you a reason to siege A.I. cities, or bring proper armies to take them.





The Settler:





They are unescorted.... why? In early game, I can see that as a tactic because your forces are spread thin.. but by mid game.... why would the A.I. send out unescorted settlers? Even if they can initially escape engagements, it's easy enough to counter. Break up your larger army, and eat the settler alive on your turn. The A.I. needs hard coding to make sure it doesn't send out a settler alone into neutral or through enemy territory.





Diplomacy:





This is currently a major exploit, but if you have your forces in friend/enemy/ally territory, the cost for declaring war should be very high to prevent backstabbing. If you do decide to backstab, then all opposing A.I. including friends and allies should treat you as a backstabber. The severity of the penalty should fade over time with good deeds, but it can never go away.





That's it for the moment.

Good ideas, especially first one. Now the siege is farce. You can just get any city if it doesn't have an army near it. Militia is mean and useless.