A new dynasty of overlords was about to appear, this time West Saxon. In 825 Ecgberht of Wessex won a decisive victory near Swindon, expelled a Mercian under-king from Kent, and annexed Kent, Essex, Surrey, and Sussex. Four years later, Mercia itself fell to Ecgberht, and even Northumbria acknowledged his lordship. This spectacular reversal, and the sudden rise of Wessex to the position of leading player, need some explanation. Two main factors may be suggested: the growing wealth of the West Saxon monarchy, fuelled by the mineral resources of recently conquered Cornwall; and the capacity of Ecgberht’s family to determine inheritance and royal succession by agreement rather than by bloodshed, which obviated one of the crippling weaknesses of earlier English kingship.