I think the whole feature of faction being immediately destroyed when their sovereign is defeated on foreign territory is making the game too easy atm 
I had a fun game going on Ridiculous difficulty, with the AI having so much troops that it was actually challenging! But then the poor bastard decides to make a countryside journey with his combat rating 200 army right through my territory. I teleport my combat rating 1000 army next to him, and there goes his 10+ city empire and countless armies up in smoke in an instant I had all my troops in this one army, while the AI had spread its troops into many, many smaller ones. I had three cities against his 10+, and his power rating was about three times higher than mine. There's no way I should win so easily.
I see a couple of solutions:
1. When an AI sovereign dies, their heir becomes the new sovereign. Would be a nice feature I think, and make the royal lineages much more important. If there's no heir, the faction is destroyed or splits into several city-states (minor factions).
or
2. Make the AI very careful about when it decides to travel in foreign territory! This isn't even the only time I've had this happen, right now the AI seems almost suicidal in its travels. Earlier in this game I even saw it travel through my territory alone! Didn't have teleport back then though.
or if nothing else works
3. Just remove the feature and let AI sovereigns retreat even if defeated in foreign territory.
I don't really like the third option, since I think the whole "Mordor crumbles when Sauron is defeated" idea is cool 
I just think it should be much, much harder to achieve (on the hardest difficulty in the game at least). Would be very cool to see both 1 and 2 implemented, and I'm sure we'll see at least no.2 when AI begins to get some updates
What do you think?
