I have been thinking a bit more about this kind of kingdom map lately when I was playing March of Empires and Thrones: Kingdom at War and came up with new ideas for the kingdom map, which is my detailed description (little further on in this topic ) maybe better explained. I will now explain the idea of this map as a comparison with March of Empires.
The alliance fortress would thus play approximately as much role as in March of Empires the capital of an area. Around this fortress are then the fortresses of the whole Alliance members distributed. The fortresses (all types of fortresses) look a bit different on the map with each level so you can see what level the fortress has. But in the alliance castle the area for the members would have to be removed, since each one has its own fortress in the realm. The whole empire is then still surrounded by a wall. (Of course, the players without an alliance are still somewhere, outside or within an area of an alliance, depends on whether the alliance wants him then "live" in their territory.) Next to it is the realm of another alliance. If you attack an opponent, you go to his castle and then attack. Then you travel there with your chosen units and spells (and of course the hero) and attack. Nothing changes in the fight itself. Other things can also be represented on the map, such as farms for food, villages for units, .... as well as places for the events. That would replace the Conquest event, since it's a "so-to-be" conquest event on the whole, because if an attacker has conquered an entire alliance territory (along with his alliance, of course) you have to submit to this alliance until you regain your independence fought for.
Further suggestions or criticisms of this idea are welcome.
PS: I have trasleted the description with Google Translate from German to English, so maybe something is not correct English. I hope you understand it anyway.