I have noticed in several of my games that some times AI civilization doesn't expand at all. He doesn't build new cities. That happened in my latest game where Siam did just this. I didn't really pay attention to it until one of my workers got near the capital and I saw that they had a great general on the city tile. As the AI never moves the general out of the city they can't produce any civilian unit and so they never expand. Don't know if this is very common but I have seen in few of my games once with England and now with Siam. They don't even have any workers and its already turn 356. Even bigger AI nations have the tendency to keep the great generals in the cities and so making the city not be able to produce civilian units. Heres the save if someone wants to check it.