By 1100, Muirchertach controlled almost all of the island, apart from the north-western territory of the
Northern Uí Néill who, under the leadership of King
Domnall Ua Lochlainn continued to remain defiant. However, as the conflict between Muirchertach and Domnall was reduced to a stalemate, Muirchertach became less committed to war and began focusing on other aspects of his rule. In the period of 1101–1112, he, like his father Toirdelbach Ua Briain, presided over the
Synod of Cashel, and was able to influence reforms in the Church, notably relating to marriage. He also enacted more laws, and reformed aspects of the justice system. He presented more gifts to the Church. Like many rulers, not only in Ireland but throughout
Europe, he seemed to realise having the
Catholic Church on his side was important to a successful reign. However, conflict with Ua Lochlainn flared again in 1112 when Domnall defied Muirchertach by marching south to
Dublin, where he burned
Fingal and carried away many captives and herds of cattle. This led Muirchertach to return once more to the North to deal with Domnall, but a peace was again organised by the abbot of
Armagh. After a month-long stand-off, matters were settled, and Muirchertach returned home to Munster. In 1114, the King became "
sick to the point of a living skeleton", and his brother Diarmuit took advantage of the High King's misfortune to steal the Kingship and banish Muirchertach. However, the next year, Muirchertach miraculously regained his strength and returned to his home, from whence he launched campaigns against Diarmuit. He finally managed to capture his rebellious brother in 1115, but his High Kingship seemed to be disintegrating. The young
Toirdelbach Ua Conchobhair, King of Connacht, son of Muirchertach's old rival
Ruadhrí na Saide Buide, and Muirchertach's nephew, at only twenty-seven years of age, was making quite a name for himself in the political landscape of Ireland. He launched repeated invasions of Munster, which Muirchertach struggled to repel in his weakened position. Muirchertach was further weakened by rebellions by the
MacCarthy Mór dynasty in southern Munster, who had been living under the rule of the
O'Brien dynasty for over a century. These rebellions were supported by Ua Conchobhair, who managed to successfully invade and partition the
Kingdom of Munster in 1118. Muirchertach died in 1119 and the
Annals of Ulster call him 'king of Ireland and tower of the honour and dignity of the western world." Munster was divided into three Kingdoms: the Kingdom of
Thomond under the O'Brien dynasty, the
Kingdom of Desmond under the
MacCarthy Mór dynasty, and the Kingdom of
Airgíalla under the Kennedys, although the last was short-lived. Muirchertach apparently went into retirement having lost his High Kingship, and died at
Lismore, modern
County Waterford, a year later in 1119. He was succeeded by Toirdelbach Ua Conchobhair as
High King of Ireland, who would prove to be one of the greatest High Kings in the
history of Ireland. Although the O'Briens never reclaimed the High Kingship, the Kingdom of Thomond remained a powerful kingdom for the next few centuries. ==Assessments==