Ronald Reagan once said, "If it looks like a duck and it walks like a duck and it quacks like a duck - it's a duck." Same thing goes with Yankees. You don't have to be born in New England to be a Yankee - at least these days.
There are certain hallmarks of the Yankee personality dating back to the ante-bellum and even the colonial period. These hallmarks are not necessarily worse these days, they have merely become larger and more confused and most folks don't recognize them as necessarily "Yankee." In fact, most folks would call these attributes liberal/progressive rather than "Yankee" but they're the same thing, actually.
1. Yankees know better than anybody else (especially you) what you need, what you should do, what you should not do and so forth. And, of course, this goes for everybody else - except themselves, of course.
2. Yankees are pure, period. Doesn't matter what they do, they subscribe to the Calvinist understanding of the "chosen" 244,000. Since they are "chosen," they can be as lawless, amoral and wicked as they please. They are, after all, (their) god's "chosen" people.
3. Yankees are arrogant (and they say that Southerners are arrogant!).
4. Yankees are mean spirited, spiteful and hateful; they have that right since they are always right.
5. Yankees are greedy and acquisitive - especially for the fruits of other folks' labor which they by rights deserve because they allow other folks to live under their benign governance.
6. Yankees believe that they should and must rule because they are appointed to do so by "divine right." They are, after all, trying to establish an earthly utopia and therefore anyone who opposes them is not "wrong" but "wicked." That is why all the horrific acts perpetrated against Southerners and the South had "God's" blessing! It was just another example of the harrowing of hell that Christ performed after His earthly death! The Yankee soldier was merely imitating Christ in bringing just punishment upon the demon South. Of course, today's Yankees don't look at it in quite that same light since they aren't even permitted by their own laws to mention "Christ." But that's okay. The understanding is the same even if the names have changed.
So you see, "Yankeeism" like the plague, spreads and academia and establishment "historians" are going to make damned sure that that doesn't change.
SWR's Lady Val