This definition of Yankee comes from the soon to be published Local
History Encyclopedia (AltaMira Press and AASLH):
PalatinoYankee:
PalatinoThe
origin of this word is murky. In 1683, according to the Oxford
English Dictionary, Yankee was in use in England as a surname,
possibly of Dutch origin. British soldiers in the New World colonies
used it as a term of contempt, however, thereafter it came to mean a
New Englander. After the Battle of Lexington, New Englanders began to
use the word themselves, even making up a mythical band of Indians, the
Yankos (meaning Invincibles) from which they claimed the word came.
The word was often used by southerners about those north of the Mason
Dixon line, often with negative overtones. Yankee was often preceded
by epithets, especially "damned." In addition, during the two world
wars the term "Yanks" was used by Europeans to describe all Americans.
For a more detailed discussion of the word, see "Yankee" in Stephen
Thernstrom, editor, *Harvard Encyclopedia of American Ethnic
Groups (Cambridge, Mass., 1980).