July 12th 927 is the closest we have to a foundation date for England, when all the kings of Britain met at Eamont Bridge, near Penrith in Cumbria, to swear an oath of peace under the overlordship of Æthelstan. Having previously been king of the Anglo-Saxons, Æthelstan’s key success in 927 was conquering Viking York which placed the kingdom of Northumbria under his control and secured the submission of the northern kings.
Æthelstan was the son of Edward the Elder, and grandson of Alfred the Great, and his ancestors had already carved large chunks from Viking lands as far north as the River Humber. As such they customarily referred to themselves as ‘king of the Saxons’ or ‘king of the Anglo-Saxons’. However, securing the submission of the other British kings meant that Æthelstan could go further. Coins minted soon after the 927 oath referred to him as rex totius Britanniae or ‘king of all Britain’.
Despite the oath, Æthelstan’s rule over the north of England was still fragile and in 937 he faced the combined forces of Scots, Vikings and Strathclyde Britons under the command of Olaf Guthfrithson, Constantine II, and Owen I respectively. An account of the ensuing Battle of Brunanburh was recorded in a contemporary poem of the same name and was preserved in the Anglo-Saxon Chronicle. A further 52 other sources mention the battle, although realistically we know little about what happened other than Æthelstan and his army were victorious. This victory secured Anglo-Saxon control, and effectively laid out the map of the British Isles as we know them today.