Here's the deal about ballads.

Take the year 1000 in Europe. It's still the Dark Ages. There are three classes of people. The self-styled nobility, churchmen and women, and the peasants. The peasants were pretty miserable.

Gradually the nobility lost their power. Because
   there weren't very many of them
   they married their cousins all the time
   their child-rearing methods were awful
   they thought they were above taking care of their lands

Over the next 600 years, there arose a middle class. Merchants with businesses, wealth, fine homes, musicians in the musicians gallery. They came to reject the idea that they were mere peasants who only deserved a short and brutish life. And by this time, their households have made ballads an established form.

If you get out a book of ballads and read a bunch of them, you will detect a common theme. That theme is "what jerks the so-called upper classes are." Whether they are abducting damsels, drowning their sisters, casting spells on their daughters-in-law or stabbing nice ploughboys in the back, they are all just a bunch of degenerates.

One exception: millers. It was all right to make songs ridiculing millers, even though they don't belong to the nobility. Millers were the used-car salesmen of the medieval period.

These theme that "They're rich but they're no good" is so appealing that there is a great pool of ballads which sloshed around Europe and over to America. And as they sloshed, they changed. The sloshing seems to have gone on for centuries, which means that the history of any one plot produces a wealth of detail. The big story (as eeen by me) gets lost.

And there you have my view of the history of ballads in a nutshell.