What was the source of the fued between the grangerfords and the shepherdsons

From the text:

"Well, I should reckon!  It started thirty year ago, or som'ers along there.  There was trouble 'bout something, and then a lawsuit to settle it; and the suit went agin one of the men, and so he up and shot the man that won the suit—which he would naturally do, of course.  Anybody would."