UKball colonized part of Northern America. The Eastern coast of North America was part of Thirteen Coloniesball, which decided to become independent because of multiple taxes from UKball.
Since he knew that it was impossible to win, USAball asked help to Kingdom of Franceball, Spanish Empireball, and Dutch Republicball. They all hated UKball and was desiring an act of revenge against him. In the point of view of these countryballs this war was just a proxy war against Britain. They gave USAball lots of guns and eventually they even sent their soldiers to help him, playing a huge part in the war.
After the victory, USAball became fully independent and recognized... But he was just a weak, irrelevant and underveloped new independent countryball in a giant world, so USAball started a long and hard journey to become the super power that he is today.