I think it would depend on what realm got invaded first. If the invaders started in Arcaea, I'd venture to say there are a lot of people who would be very slow to respond, hoping that Arcaea would take a mortal wound before anyone could show up to help. And don't rule out the importance of personal grudges in how people would act.
Heh. Possible, though I'd hope that people would think twice about letting Invaders get a foothold. Arcaea's the one exception though, I think any other realm getting Invaded first would get (relatively) quick support.
