Donnchad Midi
The reigns of Domnall and his successor, Niall Frossach of the Cenél nEógain, had been relatively peaceful, but Donnchad's rule saw a return to a more expansionist policy directed against Leinster, traditional target of the Uí Néill, and also, for the first time, the great southern kingdom of Munster.
Domnall was reckoned High King of Ireland from 743, when he defeated and killed Áed Allán of the northern Cenél nEógain branch of the Uí Néill, until his death on 20 November 763.
Domnall was eventually followed as High King by Áed Allán's younger brother Niall Frossach, who was apparently without rivals.
The succession to the kingship of Clann Cholmáin, the branch of the Uí Néill to which Domnall and Donnchad belonged, was altogether less peaceable.
[1] Donnchad's distant kinsman Fallomon mac Con Congalt of Clann Cholmáin Bicc appears to have held the title king of Mide at his death in 766, so that Donnchad can at most have been king of Uisnech, chief of Clann Cholmáin, at his father's death.
That year Donnchad defeated the Fir Tulach Midi, a minor people who lived by Lough Ennell and the following year, with the support of Fallomon mac Con Congalt, he defeated and killed his own brother Murchad at Carn Fiachach, near present-day Rathconrath, County Westmeath.
Another possible cause for, or sign of, Niall's fall from power appears in 771 and 772 when Donnchad campaigned in the lands of the northern Uí Néill.
[12] The only evidence that Donnchad may have been High King before Niall Frossach's death comes in 778 when he is said to have proclaimed the "law of Columba" together with Bressal, Abbot of Iona.
[14] In 779 Donnchad campaigned against the northern Uí Néill once again and received the submission of the "king of the North", Domnall, son of Áed Muinderg.
[16] Later in the year a meeting between the Uí Néill and the Leinstermen was held, and the King of Tara is believed to have settled whatever dispute had provoked the raid.
[17] In 784 a similar meeting appears to have been planned between Donnchad and Fiachnae mac Áedo Róin, the King of Ulster, at Inis na Ríg, one of the islands that gave modern Skerries its name.
This appears to be related to the following entry in the Annals of Ulster, which reports that Donnchad defeated the Síl nÁedo Sláine at Lia Finn, near to modern Nobber, killing Fogartach mac Cummuscaig, the king of Lagore.
[20] The óenach Tailten may have seen further trouble in 791, for Donnchad attacked Áed Oirdnide and drove him from Tailtiu and out of the valley of the river Boyne.
The Félire Óengusso, written at Tallaght in the borderlands of Leinster, apparently includes him among the oppressive secular rulers whom the authors dismissed as at best unimportant and at worst wicked.
Donnchad is less certainly believed to have been married to one Fuirseach, daughter of a Dál nAraidi king named Congal, said to have borne him Conchobar.
