How rude, especially about Indiana.
They never found out where the people were going in their BMWs
The only descriptions of the locals were entirely without sympathy.
If this is how Icelanders [edit: Greenlanders, duh!]are treated by Danes, I suggest selling out to Trump!
In English, the word American refers to someone from the United States, and almost all of the languages of the world use some equivalent term: amerikkalainen, Amerikaner, Américain, americano, американец, アメリカ人, أمريكي
When speaking South American-inflected Spanish, you might use the word estadounidense and not americano
USAian is not a word that anyone uses. I don't make the rules.
If it makes you feel better, you can tell yourself that American is just a short way of saying United States of American, if you want.