I've noticed after you take an AI faction's last city, they aren't eliminated from the game until the next turn. This allows the player to take the last city, then take the AI for all they are worth in exchange for a truce (get them to give their remaining strategic resources, technology etc). The faction is then eliminated from the game next turn.



Since the faction is already defeated, the truce is meaningless and the only result is free resources/tech for the player. My suggested solution is to eliminate the faction from the game as soon as the last city is taken.

My suggestion would be to change the AI so that it will not accept any diplomatic deal unless the AI controls at least one city at the end of the deal.



I think it's probably fine for the AI to accept a truce if the deal involves getting a city back. Also, I imagine that eliminating players at the end of a turn rather than mid-turn was a conscious decision taken for specific reasons. (Those reasons may or may not include: giving the player a chance to retake their city on the same turn if they have an army in range, and technical problems that could be caused if that player was already in the middle of another battle when their armies suddenly evaporate.)