By what Means and with what Success Did the Kings of Wessex Become Kings of England in the Tenth Century?

By What means, and with what success, did the kings of Wessex become kings of England in the Tenth Century?
In 973 Edgar 'the Peaceable' took part in a second coronation. This process was a sequence by which Edgar's superiority was recognised by the Celtic and Scandinavian rulers in the British Isles . But what events lead to this declaration of power? And if as the evidence states, Edgar was recognised as 'King of the English', then to what extent was his power secure?
The existences of Mercian and Northumbrian kingdoms were a constant threat, due to the aggressive policies pursued by rulers during the tenth century. Especially when one considers that Northumbria was an area of Viking power, who would willing give harbour to Viking raiders. Viking raids had plagued the island for centuries, and influenced the policies and style of kingship Edgar's forbearers developed. The role of Alfred the Great in instituting several policies laid the ground work for a growing West Saxon kingdom, such as the eventual annexation of Mercia by the Edward the Elder in 918. From 899 to 1016, seven direct descendants of Alfred ruled, this continuity of succession meant that the reigns of Alfred's sons could continue the work started by their father.
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