What's so hard to understand that if I'm at war with a realm, I should fight them?
If you wanted to help Luria Nova, then you'd ally with them. Why haven't you?
The only reason you are complaining about this now is that you think that with your help, Luria Nova could have won a battle they will otherwise lose. If Astrum had a big enough force that they would kick Luria's ass, even with your troops there to help, you wouldn't be complaining. And if you did get dragged into the battle, you'd be here complaining that if you had wanted to help LN, you'd have allied with them. Or if you were at war with both, you'd be complaining that the battle system put you on the wrong side, and you really wanted to fight against the other guy. The way the system is now, it's clear and unambiguous so long as you know the four steps of the process.
You have to learn the to play the game according to the way the game understands the rules. It can't read your mind and divine your intentions. The system is very simple. There are only four steps. I only took so long to describe it because I wanted to use examples and make sure it was clear. If that's too much, I'll distill it down to four simple steps:
1) Who's the defender?
2) Does anyone want to attack them?
3) Does anyone want to help the Defender?
4) Does anyone want to help the Attacker?
That's it. In the situation you describe, Helyg Derwyddon doesn't fit in any of those categories. They're only at Peace with the defender, so they aren't willing to join in battle to help them. (If you wanted to risk your life to help, you'd be allies.) They are also not at war with the defender, or allied to the attacker. So they don't join in on that side either. They pop the top off a couple beers, grab some popcorn, and watch the fight.
FWIW - This four-step sequence is why rogue units always side with the attacker and never the defender. And if a rogue unit is defending, no one ever lines up with them. Two realms at war will all line up as attackers against them.
