In warband, it's quite normal to see a wandering enemy army in your kingdom, and nobody following it. This is kinda highly unrealistic, because if I was a king at that time and there was an army of 200 sarranids running around unchecked, I'd be a little ticked and send some guys after it. What i'm saying is that kingdoms should be less casual about other kingdom's troops running around in their land. Possible balances:
-Allowing a nation's vassals to have full view of enemy vassals in their kingdom (kinda unrealistic)
-Warning a nation's vassals when enemy vassals are near them
-Having increased line of sight in one's own kingdom that they are a vassal in
-Having allied lords/cities send out large patrols to kill the enemy when they are in the cities' land
This would make for more strategic gameplay, I.E. a faction would gradually work it's way to a major city, instead of going in, capping it, and having no support from nearby castles because they didnt cap those previously.
Tell me what you think.