Besides including information on Kentucky to the right in the Dictionary list, I also found this article from 1959 which points to the history of Kentucky as "dark and bloody ground" - a key theme in the play.
Monday, May. 25, 1959 Dark & Bloody Primary
Decades of warfare between the Iroquois and Cherokee gave Kentucky its name, the "dark and bloody ground." The tradition of bloodthirsty cunning has survived with a vengeance in Kentucky politics, turned vote-hunting into a boyhood sport, factional throat-cutting into a party game that everybody enjoys.
Continued at the following link but the rest is not as pertinent to the play: