Modern historians believe this scheme was crafted in the 8th century from the various genealogical traditions of powerful dynasties, and intended to justify their status by projecting it far into the past.

Each king ruled directly only within the bounds of his own petty kingdom and was responsible for ensuring good government by exercising fír flaithemon (rulers' truth).

His responsibilities included convening its óenach (popular assembly), collecting taxes, building public works, external relations, defence, emergency legislation, law enforcement, and promulgating legal judgment.

A second sign that sacred kingship did not disappear with the arrival of Christianity is the supposed lawsuit between Congal Cáech, king of the Ulaid, and Domnall mac Áedo.

Congal was supposedly blinded in one eye by Domnall's bees, from whence his byname Cáech (half-blind or squinting), this injury rendering him imperfect and unable to remain High King.

In 1002, the high kingship of Ireland was wrested from Mael Sechnaill II of the southern Uí Néill by Brian "Boruma" mac Cennédig of the Kingdom of Munster.

The most successful of these early dynasties were the Uí Néill (encompassing descendants of Niall of the Nine Hostages, such as the Cenél nEógain), who, as kings of Tara, had been conquering petty kingdoms, expelling their rulers, and agglomerating their territories under the direct rule of their expanding kindred since the fifth century.

Its clerics developed the theory of a high kingship of Ireland and wrote tracts exhorting kings to rule rather than reign.

In return, the paruchiae (monastic federations) of the Irish church received royal patronage in the form of shrines, building works, land, and protection.

[13] By the twelfth century, the dual process of agglomeration of territory and consolidation of kingship saw the handful of remaining provincial kings abandoning the traditional royal sites for the cities, employing ministers and governors, receiving advice from an oireacht (a body of noble counsellors), presiding at reforming synods, and maintaining standing armies.

These compact families (the Uí Briain of Munster, the Meic Lochlainn of the North, the Uí Conchubhair of Connacht) intermarried and competed against each other on a national basis so that on the eve of the Anglo-Norman incursion of 1169 the agglomeration/consolidation process was complete and their provincial kingdoms divided, dismembered and transformed into fiefdoms held from (or in rebellion against) one of their number acting as king of Ireland.