Funny that, I didn’t have to explain to anyone what it is because the immediate reaction by people like you was "that’s not how you say ‘American’ ".
You could have called them anything and I would have known what you were talking about because of the context. The same context you used to guess “USAian” was available to everyone else.
So it was context alone, was it? Using the acronym USA in an adjective referring to something from the USA didn’t clue you in at all. Just the context. Without it your reasoning would’ve completely led you astray and the sentence would’ve become unquestionably incomprehensible.
You could have called them anything and I would have known what you were talking about because of the context. The same context you used to guess “USAian” was available to everyone else.
So it was context alone, was it? Using the acronym USA in an adjective referring to something from the USA didn’t clue you in at all. Just the context. Without it your reasoning would’ve completely led you astray and the sentence would’ve become unquestionably incomprehensible.