Now, using "Americans" to refer to everyone over here did exist before the U.S., going back to at least the 1500s. I think that was only in use in English, I've never looked up what was used in French and Spanish back then. But since the USA came into being as country, it has been the default term for US citizens colloquially.
Confidently wrong. US leaders didn't start referring to its citizens as americans or its country as america until ~1900.
I know you won't read the book I linked, and are going off of white-supremacist vibes, so here's an article for everyone else about the history of this imperialist usage.
Getting you to read is impossible. Stop white-supremacist vibing and actually read about its historical usage. I even linked you an article, which I know you didn't read.
It's so frustrating to read books about the long history of these things and then have confidently wrong children try to correct you with a vibes-based analysis.