This problem is one of the most annoying things in the game.As i remember speaking of this in another thread who had to do with this kind of invasion,i must say that they sould have changed this with C3C or with a patch.It cannot be that every time that AI wants to build a city or make war against someone it has to pass throught my territory.It is rediculus,neither i can declare war each and every time a unit comes into my territory.And AI never asks for a right of passage aggrement.I just hate this.