Well, it came down to picking their allies: Vix and Perdan, or Highmarch? The rest were irrelevant. Heck at first, it was really: Highmarch or Perdan?
But Edvard had too much resentment for Caligus. He was unwilling to give them anything, even if he had no say in that, given all the ceded lands currently belonged to Highmarch, and Highmarch was going through with it regardless.
It wasn't just a bad move because they'll lose regions out of it (and possibly their entire existence if they keep at it), but they are also alienating their most devout ally: Highmarch. Highmarch was willing to give more to the North so that Fallangard wouldn't have to. It was willing to put the whole treaty, and thus its survival, in peril, just to give Fallangard a chance. It then went to great pains to tiptoe around Fallangard.
Highmarch showed more dedication to Fallangard than it could ever expect from the realms it chose to stay aligned to. They chose to be Vix's tools rather than remain Highmarch's brothers. They didn't have to betray Highmarch, they chose to. Staying completely neutral in the conflict was totally a possibility. As was soloing Caligus.
Edvard had a lot of choices, and all of them were better for Fallangard than the one he picked. Attacking Highmarch directly, and continuously escalating the pressure against them... was a bad move, all-around.
