With over 500 hours playtime, I have experienced every faction there is in this game and have never seen anything like the Norsca campaign (Mortal Empires). EVERYTIME you confederate with either World Walkers or Wintertooth, you get 6-10 declarations of war the following turn. Then Empire, Dark Elves, High Elves and Dwarves all leave their homelands undefended to launch one giant crusade against you. After that, the campaign is pretty much done since you won't be leaving your starting area ever again because you're so busy defending. I can not imagine this to be intentional since no other faction has a similar issue / feature. I do not know for sure why the AI is so overly aggressive towards Norsca but I believe it just interprets the sudden confederation power spike as an extreme threat. This totally killed the fun for me and pretty much feels like the opposite of what Norsca gameplay should be (Viking Raiders). It does not render the faction unplayable but hardly enjoyable and should be fixed asap in my opinion.
Also, why are good/order factions (Empire, High Elves, Dwarves) always an auto win on any difficulty and evil/chaos factions sometimes feel really difficult even on normal (Beastmen, Norsca, Orcs)?