American Citizen

This term is commonly used in United States to identified a U.S. Citizen.  Wrong.  Everyone from Alaska to Argentina is an American Citizen since America is not a "Nation" but a "Continent".  Venezuelans, Mexicans, Dominicans, Colombians, Canadians, Brazilians and many others are all "American Citizens" because they all are from the continent named "America".  The Germans, Italians and other citizens from Europe are not called "European Citizens".  They are named after the individual nation they are from.  In the United States we have a U.S. Passport and not an American Passport.  Then... Why "American Citizen" and not "U.S. Citizen"?