I've always wondered about the infamous feud between the Hatfields and McCoys, celebrated in song and story, and by chance, I happened on an explanation the other day. To research a possible novel set in eastern Kentucky about the WPA during the 1930s, what better place to start than the relevant state guide published by the WPA? (The WPA sponsored guides for every state, and they're gold mines of information.) Following the index entry for "Feuds," I learned that sometime during the early nineteenth century, on a certain Election Day, a young man from the Hatfield clan in what would now be West Virginia eloped with the daughter of a McCoy from Kentucky. Sometime later, he returned her, unwed, with a child.
War broke out between the clans. "The feud," reports the WPA guide, "outlived all of those who saw its beginning, and though there were peaceful interludes, a trivial argument over such a matter as the number of notches on a hog's ear would start another series of killings." Because the participants came from different states and fled from one to another, the authorities were either impotent to stop the violence or didn't try hard enough. However, when one Hatfield was hanged for a particularly gruesome series of crimes, legend says that 6,000 spectators attended.
Source: Kentucky: A Guide to the Bluegrass State, 1939, p. 434.