Sounds great. The ensuing wars could've been enough to convince that Arman and Arhus should unify down the road, so they could've entered the union right afterwards as a result of ultimately losing. 

I'd think Arman or Arhus would pull ahead early on, though. Since they fight traditionally and were probably a bit bigger. Fairly well trained. Be a good explanation if you wanted a reason your military is devious; they found a way around the traditionalism and eventually won, or beat them back with no clear Victor. Or whatever we're going with.