Actually there’s absolutely no mention of Americans or any other nationality, and the world the movie is set in looks like 19th century europe but is in reality a fictional, fairy-tale-like world.
True.
What about the fact that both warring governments wanted Howl (a powerful wizard) to fight for them, and they tried to order him to do that?
Also, doesn’t it seem like government breeds the conflict in the film? After all, it all started when a prince went missing. I thought it showed how government == evil very well.