I’ll take a stab at this - the land where each original colony was mapped out - that was called America, was it not? After Vespucci who charted the Americas.
Americans living in one of the original 13 colonies came together and decided they wanted to govern themselves instead of being subject to the monarchy overseas.
Once the Declaration of Independence separated us from England, we were called the United States of America.
Just my thoughts.
Quite right, of course. And that was the root cause of the ‘disagreement’ with King George. He - and most Britons -considered the colonists subjects of the crown. The colonies beggged to differ and fought for their independence from Briton. They were Americans.