In the early day, the word "Yankee" was mentioned to people from New England, where is the first developing area of the United States.
Later, Yankee was mentioned to people from the North East area and finally, it includes all American people.
Like other words, the origin of Yankee is unclear but the most reasonable source is that it is distorted from the popular Dutch name "Janke" means "little John."
There were evidences at the time that English army call Americans "Yankee" During the Civil war, the word Yankee became sensitive when it is used by the Federation from the South to call the Union from the North.
However, now the internal wars are done. The word Yankee is not used to seperate the nation anymore. It is now represented the whole American.