Well.
First off, in relation to the stat system this is what we's in the industry call making a mountain out of a mole hill. The stats don't directly mean anything, they are purely an abstract representation of each state's military organisation. A state with 0% could still win against one with 100%, if they play their cards right. And don't worry about favouritism; I hate everybody equally so you don't have to worry there.
As for Japan, I'm going to have to say no. All foreign powers will be NPCed for plot and balance purposes. Sorry, but there are reasons.
Come to think of it clock, I forgot something very important in your app. Read the rules plz.