In 802 the fortunes of Wessex were transformed by the accession of Egbert who came from a cadet branch of the ruling dynasty that claimed descent from Ine's brother Ingild. With his accession the throne became firmly established in the hands of a single lineage. Early in his reign he conducted two campaigns against the "West Welsh", first in 813 and then again at Gafulford in 825. During the course of these campaigns he conquered the western Britons still in Devon and reduced those beyond the River Tamar, now Cornwall, to the status of a vassal. In 825 or 826 he overturned the political order of England by decisively defeating King Beornwulf of Mercia at Ellendun and seizing control of Surrey, Sussex, Kent and Essex from the Mercians, while with his help East Anglia broke away from Mercian control. In 829 he conquered Mercia, driving its King Wiglaf into exile, and secured acknowledgement of his overlordship from the king of Northumbria. He thereby became the Bretwalda, or high king of Britain. This position of dominance was short-lived, as Wiglaf returned and restored Mercian independence in 830, but the expansion of Wessex across south-eastern England proved permanent.