More people, less space, produced a great deal of turmoil for those Celtic tribal groups that were driven into those western mountains. Defending the family's land and honour were a constant activity, especially when an insult from another family group was presented. "Eye for a eye, tooth for a tooth", was the common standard, and a tribal "feud" could last for generations.
It appears that Roman law started the concept of individual rights. Their term "iniuria" (injury) embraced an event where someone purposely disregard another's rights or personality. This usually involved some form of injury, or even death. In the place of returning equal retribution, a compensation was made to the victim or his/her family. Of course, this compensation varied according to the status of the victim. In Celtic culture, influenced by Roman laws, a "compensation payable" was called "sarhaed". When homicide was involved, this became a specific compensation called "galanas". This was the ancient Briton's attempt to limit death and destruction among the family groups and control vengeance (feud). The compensation for killing depended on the status of the victim, and the liability was spread among the kindred. Thus, if someone in your tribe killed, you would be held responsible, down to the forth cousin! So a Welsh name, gave your descent through six generations. If you were descended from a common 4-generation grandfather, then you had to pay into the compensation. What's in a Welsh name? Your liability and status!
A most important reference is: "Hywel Dda, The Law", translated and edited by Dafydd Jenkins, Gomer Press, 1990, the "galans" (p. 346), the "sarhaed" (pp. 379-380).