Awarded upon completion of the Hordafylke arc.
This arc is avaiable towards the latter end of the game, and is started the same way as the other regions; by pleding to the area at the alliance map. It's at the bottom right of the main England map.
It's all fairly straight-forward, but there are some hints below in the spoiler tag.
If this is not available then chances are you are yet to speak to Sigurd. He's in the room joint onto the map room, go in and speak to him and he'll talk about going back to Norway