Edward the Elder had conquered the Danish territories in Mercia and East Anglia with the assistance of Æthelflæd and her husband, but when Edward died the Danish king Sihtric still ruled the Viking Kingdom of York (formerly the southern Northumbrian kingdom of Deira).

Æthelstan in January 926 had arranged for one of his sisters to marry Sihtric.

The two kings had agreed not to invade each other's territories or to support each other's enemies.

Sihtric dies the following year and Æthelstan seizes the chance to invade.

Guthfrith, a cousin of Sihtric, leads a fleet from Dublin to try to take the throne, but Æthelstan easily prevails.

He captures York and receives the submission of the Danish people.

According to a southern chronicler, he "succeeded to the kingdom of the Northumbrians", and it is uncertain whether he had to fight Guthfrith.

Southern kings had never ruled the north, and his usurpation is met with outrage by the Northumbrians, who have always resisted southern control.

However, at Eamont, near Penrith, on July 12, 927, King Constantine of Scotland, King Hywel Dda of Deheubarth, Ealdred of Bamburgh, and King Owain of Strathclyde (or Morgan ap Owain of Gwent) accepts Æthelstan's overlordship.

His triumph leads to seven years of peace in the north.