The term "red neck" originated from a conflict that did not concern black slavery; it related to the "right of the coal miners to belong to a union."
The original "red necks" were a group of workers who assembled along Blair Mountain in West Virginia in the summer of 1921 to take action in response to the death of Sid Hatfield, the slain police chief of Matewan; he was unarmed when he was gunned down on the steps of the McDowell County Court House, where he was scheduled to go on trial. No one knew exactly who killed him, but the mine-owners often employed the services of the Baldwin-Felts Detective Agency to use strong arm tactics to establish and maintain power; so they would have been natural suspects, and the local people considered them to be thugs.
Btw, this discussion has gone way off-topic from Avril Lavigne's Girlfriend issue.