Who were the Hatfield's and Mccoy's and what was the cause of their feud? (This was a true event, people)

During the most heated years of the feud, each family was ruled by a well-known patriarch. William Anderson Hatfield, known as "Devil Anse," had the appearance of a backwoods, rough-hewn mountain dweller. By the 1870s Devil Anse was an increasingly successful timber merchant who employed dozens of men, including some McCoys. On the other side of the feud stood Randolph "Old Ranel" McCoy. Though not as prosperous as Devil Anse, Randolph owned some land and livestock. Both families lived along the Tug Fork of the Big Sandy River, which snaked along the boundary between Kentucky and West Virginia, and both families had complex kinship and social networks. Family loyalty was often determined not only by blood but by employment and proximity. The families even intermarried and sometimes switched family loyalties, even once the feud had started.

Each family owned a large amout of land and animals for farming. They were now as "Royalty" at the time and in the area. They, of course both being "Royalty", tried to outdo each other to be the overall "Royal" Family.