People from The United States should/must be called United Statians instead of Americans in order to avoid ambiguity in meaning. Strictly speaking, any person born in the Americas is an American; e.g. people from Brazil, Argentina, Chile, Mexico, Canada and the other corresponding countries lying in the Americas. Follow the links below to know more.
http://en.wikipedia.org/wiki/United_Statians
http://www.urbandictionary.com/define.php?term=United%20Statian
http://en.wikipedia.org/wiki/United_Statians
http://www.urbandictionary.com/define.php?term=United%20Statian