Happy Independence Day, imperialist stooges.
The history of the term Yankee, or Yank, appears to largely be in dispute, with Oxford admitting that the definite origin of the word remains unclear. However, there are a couple popular theories.
One common etymology of Yankee holds that it came from a slanderous term that Dutch settlers in America used for English Colonists. They derisively referred to the Brits as Little John, or Janke, and the name stuck as yanks.
Conversely, two popular surnames for the Dutch during the colonial area were "Jan" and "Kees." This eventually turned into a contemptuous name for Dutch settlers in the northeast, "Jankies," which finally evolved into Yankees, a term applied from anyone from the American northeast or even to citizens of the United States itself.
Sources:
http://en.citizendium.org/wiki/Yankee
http://www.etymonline.com/index.php?term=Yankee
