Here are the Regions of England, Scotland and Wales, Size does not matter, whats the point of having a large region in your control if you can't defend it?
Incorporated into this game is a Unique Land ownership system, similar to that of the Feudal system this would be paired with the AI Lord system, note All land at the start of the game will be owned by NPC’s You can establish a settlement and you can claim Independence from the NPC Lord, this could cause the Lord to attack your settlement, if the NPC lords castle or fort is captured the control of the Province would be given to the conqueror.
Once a Settlement has claimed independence the area around it belongs to the lord of the settlement.
Also note the Regions are split into Provinces, Like North west would have about 15-20 Provinces, the AI Lord at the start of the game is in complete control of them, most of them are not developed Meaning you can found a settlement and take control of a province by declaring 'independence'
And then you can conquer the other provinces till you take control of the main town of the region thus controlling the region.