Towards the middle of the 8th century Strathclyde was again threatened by an alliance between the Northumbrians and Picts, and in 750 the Northumbrian king Eadberht wrested from them a considerable part of their territories in the west including Kyle in Ayrshire.
There may be the folk-right of West and East Saxons, of East Angles, of Kentish men, Mercians, Northumbrians, Danes, Welshmen, and these main folk-right divisions remain even when tribal kingdoms disappear and the people is concentrated in one or two realms. The chief centres for the formulation and application of folkright were in the 10th and iith centuries the shire-moots, while the witan of the realm generally placed themselves on the higher ground of State expediency, although occasionally using folkright ideas.
But in 957 the Mercians and Northumbrians revolted and chose Edgar as their king.
He succeeded his brother Edmund in the year 946 and at this time received the formal submission both of the Northumbrians and Scots.
The latter had just crossed from Ireland and had been chosen king by the Northumbrians, who threw off their allegiance to Edmund.