It is clear from the annals that internal dynastic rivalry was pervasive, and it gets extensive coverage. Within families, succession to the chieftainship was often achieved through conflict between rival claimants, with subservient families often splitting to side with one or other claimant, resulting in even more conflict. In the early 1500s, we learn that

(1502) “The defeat of Tulach-finn, in Glen-Eidhnighe, was given by the sons of Turlough Oge, the son of Turlough, son of Niall Roe, to O'Boyle, their paternal uncle, i.e. Niall Boy, where O'Boyle himself and his two sons, Rury and Donnell Ballagh, and others, were slain. It was O'Boyle himself that had plotted a snare against the sons of Turlough, by which he himself was killed.

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And a few years later

(1509) “O'Boyle (Edmond Boy, the son of Niall) was slain at night, with one cast of a javelin, at Luachros, by Conor Oge O'Boyle.”

It takes time, but they eventually get their revenge:

(1530) “Conor Oge O'Boyle, Tanist of Boylagh, was slain by the sons of O'Boyle (Niall, the son of Turlough), on the Leacach, on the 6th of January.”

“Felim, the son of Conor O'Boyle, was slain by the sons of O'Boyle.”

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A generation later, things are still contentious:

(1539) “Niall Oge O'Boyle was slain by Conor, the son of O'Boyle”

(1543) “The son of O'Boyle (Brian, the son of Niall, son of Turlough) was treacherously slain by the sons of Niall Oge O'Boyle, who were in his friendship, in his company, and in his pay.”

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Not only distant cousins, but also brothers, met gruesome ends:

(1540)” The two sons of O'Boyle, Niall Roe and Conor, were in contention and at strife with each other. Niall made an incursion against Conor into Loughros (for Conor had his seat and residence there), and remained that night in ambush in the church of St. Seanchan. Conor next morning went upon the hill adjacent to the church, and Niall and his people sallied forth from the church against him. When Conor saw them approaching him, he ran away to avoid them, as he had with him only a few and these persons unfit to bear arms, and he proceeded alone down across the strand of Loughros. Niall pursued him as quickly as he was able, and he outran his own people in his eagerness to catch Conor; he overtook him, and they engaged each other vigorously and ferociously, forgetful of friendship and relationship. Conor gave Niall a blow on the top of the head, and prostrated him on the ground, and then fled away, severely wounded. His people came up to Niall, who told them to pursue Conor, and that he himself was not in danger of death on that occasion. They did so at his request, and overtook Conor on the borders of a neighbouring lake; and they did not dare to come to blows with him, until they had first knocked him down with the stones which were on the strand of the lake; and when he was prostrated, they struck at him with weapons. And on their return they found Niall dead. There had not been of their tribe, for some time, two of the same ages who were more generally lamented than these two who were slain by each other.”