Battle of Brunanburh
The Battle of Brunanburh was fought in 937 between Æthelstan, King of England, and an alliance of Olaf Guthfrithson, King of Dublin; Constantine II, King of Scotland; and Owain, King of Strathclyde. The battle is sometimes cited as the point of origin for English national identity: historians such as Michael Livingston argue that "the men who fought and died on that field forged a political map of the future that remains, arguably making the Battle of Brunanburh one of the most significant battles in the long history not just of England, but of the whole of the British Isles." Following an unchallenged invasion of Scotland by Æthelstan in 934, possibly launched because Constantine had violated a peace treaty, it became apparent that Æthelstan could be defeated only by an alliance of his enemies.