After the invasions of the 890s, Wessex and English Mercia continued to be attacked by the Danish settlers in England, and by small Danish raiding forces from overseas, but these incursions were usually defeated, while there were no further major invasions from the continent. The balance of power tipped steadily in favour of the English. In 911 Ealdorman Æthelred died, leaving his widow, Alfred's daughter Æthelflæd, in charge of Mercia. Alfred's son and successor Edward the Elder, then annexed London, Oxford and the surrounding area, probably including Middlesex, Hertfordshire, Buckinghamshire and Oxfordshire, from Mercia to Wessex. Between 913 and 918 a series of English offensives overwhelmed the Danes of Mercia and East Anglia, bringing all of England south of the Humber under Edward's power. In 918 Æthelflæd died and Edward took over direct control of Mercia, extinguishing what remained of its independence and ensuring that henceforth there would be only one Kingdom of the English. In 927 Edward's successor Athelstan conquered Northumbria, bringing the whole of England under one ruler for the first time. The Kingdom of Wessex had thus been transformed into the Kingdom of England.