One who is born in the United States of America is defined as a United Statesmen, just as one who is born in Canada a Canadian and one who is born in Mexico is a Mexican. All Canadian, Mexican and a United Statesmen can be called Americans.
1) A person born in any of the 50 states of the United States of America is a United Statesmen.
2) A person born in Canada is not a United Statesmen.
3) A person born in Mexico is not a United Statesmen.
4) An American can be Canadian, Mexican, or United Statesmen.
5) A United Statesmen is specific to its region of North America.
Luca: Ezekiel, what think you about the United Statesian Occupation in Iraq?
Ezekiel: Mmmm... easy to say. A big split-up by an avaricious and selfish man, thus, George W. Bush.
Ezekiel: Have you heard of the party at Fatima's house?
Luca: No... was there one?
Ezekiel: Yes! it was full of United Statesians, Canadians and Brazilians.
An incorrect term applied to citizens of the United States of America generally out of anger that they would presume to call themselves Americans. The politically correct term would be United States Citizen. The proliferation of the term American (often by members of other North and South American nations) to refer to such people has made it appropriate to do so.
A phrase used to disambiguate between people living in the United States and people living in the continents of North or South America, since "American" can refer to either group of people.
When talking to people who have this phrase in their vocabulary, "United Statesian" always refers to only people living in the United States, while "American" always refers to people living anywhere in North or South America.
Jack: Dude, Americans are so fucking stupid.
José: Wtf dude
Jack: Sorry, I meant United Statesians.
José: Oh okay :)