 During the latter part of his reign, Bréifne took part in campaigns against the Norman invasion of Ireland.His assassination by the Anglo-Normans in 1172 was followed by a succession dispute, and a conflict between the Ua Ruairc and Ua Raghallaigh (O'Reilly) dynasties.Following the Battle of Magh Slecht in 1256, Bréifne split into West Breifne (ruled by the Ua Ruairc) and East Breifne (ruled by the Ua Raghallaigh).