Makes no sense to you, perhaps, but it makes enough sense to enough people to try it regardless of penalties and consequences.
"litterally nothing to gain" if rather relative. They obviously found reasons to.
The players there, or in Astrum or Iashalur or wherever, may disagree. If they do, you are wrong. You don't get to be judge of what makes sense for other players.
The northern realms have plenty of reasons to see Aurvandil attacked or destroyed. They just don't have anything to do with "Aurvandil can put an army on my border next week". And that doesn't mean their reasons are invalid, either.
Fallacy, Fallacy, Fallacy.
Why do y'all act like I'm trying to comment on other's gameplay?
I'm not. What I'm trying to do is perhaps give you some reasons to consider, and help fill in some of the possible reasons that this may be the policy that Tom has implemented. So he doesn't have to write out a detailed explanation to everything, perhaps I'm just writing out what I suppose to be some of the many cases.
If someone jumps off a cliff and gets upset that they broke their leg, and asks why this is the case, and simply gets told that such is wrong and shouldn't be done. Then, still wondering why, they continue to jump off cliffs hurting themselves regardless of consequences or being told that such isn't intended, both by obvious world-created consequences then they are the ones doing something wrong. You don't need an explanation to know that if you're getting hit with repeated penalties to see that "hey, perhaps what I'm doing isn't correct."
I can come up with reasons why people are trying to fight this war. Whether they are correct or not, I don't know but some of them certainly make sense. I'm not judging people, but I can understand why some of these behaviors are better or worse for game health long-term. Also note, this list is only for those realms NORTH of the D'Hara/Terran/Luria Nova line.
1. They are bored and want someone to fight.
2. They've created a permanent peace lock, and so they literally can't fight anyone else than someone so far south, without risking a gang-bang for breaking the peace.
3. They don't want to fight another SA realm. (Doesn't make sense to me, as Christian nations fought and fight all the time, but not for me to judge).
4. They are losing nobles, and need someway to try and keep them around. (See #1)
5. Allies asked them to. (See #2)
6. Religious fight against "heathens"
7. They are a threat to SA. (Simply not true, because they themselves can't expand to encompass the whole island)
The question though is, does it really matter why the north is fighting Aurvandil? NO! It doesn't. What matters is that the game discourages you from doing it, because this course of action and thinking protects game play situations which lead to toxic atmospheres. It is a defense against toxicity and exploits so that a single group of players can't ruin the fun for everyone else. This is what I believe is the primary reason, but no one seems to want to address that. It is also why I believe we should look as to what the other causes are here because that will indicate perhaps why such wars are discouraged highly.