Walter Liath de Burgh

https://en.wikipedia.org/wiki/Walter_Liath_de_Burgh

Burke Civil War
De Burgh aggrandized the lordship of Connacht to himself and so a battle broke out between him and his cousin, William Donn de Burgh, Earl of Ulster, for power. Warfare continued until November 1331 when the Earl captured Walter and his two brothers, imprisoning them in Northburgh Castle, County Donegal. Walter died there of starvation in February 1332.

Walter's sister, Gylle de Burgh, planned revenge on the earl. She persuaded her husband, Richard de Mandeville, and John de Logan to murder William Donn in Carrickfergus on 6 June 1333. This death was a catastrophe for the Anglo-Irish colony, as within six months all Ulster west of the Bann was lost, while Connacht descended into factionalism. For over two hundred years it would remain largely outside the realm of the Dublin government. It was these deaths that would begin the Burke Civil War.