So I thought about it a bit.
Maybe the two countries/nations/whatever that our characters come from have kind of been enemies for a long time. Or, at least, have had a few wars before. The third country hasn't seemed to. But the war that happens now, between the three, is maybe orchestrated by the third? I was thinking the third might have a very different type of magic, say believing it comes from a certain god that our countries don't have, and believe they should destroy the other two countries? And thus orchestrated this war.
It's just an idea.
Also country wise I think we should have freedom to create each of our own (however much details we want for it, haha) and magic wise I think it would vary by nation basically. Nothing too powerful/OP, of course. I have a few ideas for what I want to do magic wise if I decided to have my character use magic.