(Disclaimer: I do not claim to own Hetalia: Axis Powers in any way.)
He was a hero and he knew it very well. America always made sure that everyone else knew just as well who the hero was. If any of the other countries knew one thing about him he made sure they knew he was the hero.
So why was it that other countries flinched at the very sound of his name? Why was Canada beaten up by his own friend? Why did England cry every time that it rained?
He knew why even though he tired to delude himself with his thoughts of heroism. Being a hero came with villains and a hero was always the worst of them all.