Athelstan, a son of Edward the Elder, conquers Northumbria and is the first to reign over a united England. Over the following years Northumbria repeatedly changed hands between the English kings and Norwegian invaders, but was definitively brought under English control by King Edred in 954, completing the unification of England.
Editors. "Kingdom of England created". The Literary Encyclopedia. First published 01 May 2009
[http://www.litencyc.com/php/stopics.php?rec=true&UID=7030, accessed 30 January 2015.]