This is a coop campaign, with my brother.
I play Middenland and he plays Thegans Errantry.
Whenever it says "Vassal" on the list to the right, it means that it is a vassal of Middenland. Nobody else has any vassals.
The most impactful mods are Radious mod, No Confederacy and the ability to vassal factions.
If you have any questions; feel free to ask.
Credits for the map goes to @Azure_Eagle