Asklemmy

Its my understanding that in Spanish, "American" refers to anyone from the Americas. In some languages/countries, the Americas are taught as 1 continent (Europe, Asia, Africa, Australia, Antarctica, and America), so a person from any country in the Americas would be called "American".

In most English speaking countries, we are taught that there are 7 continents, and north and south America are separate continents. In that context, you wouldn't really use a term to refer to people from both continents. It's similar to how, as a spaniard, I could not call you "eurasian", i would just say "european". In English, you would then have to refer to people as either "north american" or "south american".

In practice, we do refer to people from south America as "south american", but north america usually gets divided into "central american" and "caribbean", which only leaves the US, Canada, and Mexico.

People from Mexico and Canada have obvious demonyms, while the USA does not. "Gringo" also applies to Canadians (and it's specifically referring to non-spanish speaking european americans), so it doesn't really work as a demonym. "Yankee" doesn't really work, either, because it only applies to a subset of people from the US, so it's similar to calling everyone from Great Britain "English".

I haven't met any primarily English speaking residents of the americas with any problem with people from the US being called "american".