From the death of Áed Allán in 743 until the overthrow of Máel Sechnaill mac Domnaill by Brian Boru in 1002, the succession to the High Kingship of Ireland alternated between northern and southern branches of the Uí Néill with the north represented by members of the Cenél nÉogain, Áed's paternal kindred, and the south by the Clann Cholmáin, his mother's kin.
[2] During the reign of Máel Sechnaill mac Máele Ruanaid, who succeeded Áed's father as High King, the balance of power between north and south which had ensured the alternating succession appeared to be tipping in favour of the southern Clann Cholmáin kindred.
In 859, Osraige was made subject to the Uí Néill, and this led to open warfare between Máel Sechnaill and Áed.
Following the death of Neill Caille in 845, Áed's uncle Máel Dúin mac Áeda assumed the kingship of Ailech.
Áed is mentioned for the first time in the annals this year, as the Annals of Ulster records that he made a foray against the Ulaid, and he left behind dead Coinnecán son of Colmán and Flaithbertach son of Niall, and a large number besides[5] Presumably Flaithbertach was his own brother, and this foray was made to secure Áed's position as king of Ailech.
The reigning High-King at the time, Mael Sechnaill, seemed more concerned with the internal Irish power struggle, particularly in Munster, than with engaging the Norse.
Máel Sechnaill now turned his attention to the north, where the growing power of Áed Findliath had become a threat against him as head of Uí Néill.
[10] Máel Sechnaill mac Máele Ruanaid died 20 November 862, and he was on that occasion described in the Annals of Ulster as ri h-Erenn uile, king of all Ireland.
That was a title that would never be used to refer to Áed Findliath, even though he assumed the kingship of Tara following Máel Sechnaill's death, and has also been counted in the lists of High Kings of Ireland.
Máel Sechnaill's successor as head of Clann Cholmain and king of Míde, Lorcán mac Cathail, allied himself with Amlaib, Ímar and Auisle against Flann of Brega.
[4] In 866 Amlaíb and Auisle left Ireland with the larger part of the Norse forces, and, in co-operation with the Norse-Gaels from present-day Scotland, they attacked the Picts.
According to the Annals of Ulster he defeated "the Uí Neíll of Brega, and the Laigin, and a large force of the foreigners" in a battle at a place called Cell Ua nDaigri.
On that occasion he was described as "king of Tara" (rex Temorie), although a poem from the annals refers to him as "over-king of the Irish" (airdri Gaidhel).