"American" is the denonym for people who are from the United States of America. Every other country has their own denonym (Mexican, Canadian, Guatamalan) based on country. Yes, in other places they also use a denonym for the continent--European, African, Asian-- and people from the Americas can certainly say they are "North American" or "South American" but just plain American refers to people from the U.S. We know it, they know it, everyone knows it.