America is like a new adult because they have broken free from the barriers as a teenager and have finally earned their independence. Also, they are now identified as a self-reliant adult, instead of an inexperienced kid.
America is like a lion because lions establish their power by hunting in packs that prey on other large animals. While the war resulted in the establishment of the Canadian border, for lions, their border is demonstrated by dominating other animals.
America is like a new band increasing in fame because they are working diligently in order to be established by themselves and through their hard efforts.