You guys are forgetting the current state of Dwilight and its politics. Only LN would have really gone to help Westfold and they are dead mostly I hear everywhere so can't effectively march that far.
Swordfell has the SA complication so won't march so quickly and maybe HD could've aided, but after the last war I can imagine they didn't want to. Avernus could've maybe helped? I don't know.
Northern realms were recovering still I think. HD just got off of their war against Morek so they probably were too exhausted. Westfold went into this war looking pretty confident but they probably did not know Astrum's military strength. Despite their military council being mediocre, they have more than enough resources to overwhelm any realm 1v1.
If Westfold didn't enter this war, I think Astrum might have suffered the fate of LN but Westfold is keeping Astrum alive by killing itself.
