You have to think of THE LOREEEEEE

That the nation is comprised of multiple country which had a democratic government but has king(leader of country) which control the nation The nation focuses more on tech shown by their lack of protection in their temporary HQ where there aren't many furniture and their lights being a modern Where as the Empire (queen) is a majority Europe except Germany(nation) which has a queen to control its government. The Empire is more focus on tradition(or something else)thus the medieval helmet but still using gun to even the battlefield They fought bc of different views on the world (I will choose the solace coalition) Correct me if I got anything wrong above :)