It depends on historical perspective. The Normans promoted the view that King Harold Godwinson of England had betrayed an oath to help Duke William of Normandy to gain the throne of England. The Bayeux Tapestry shows this but has no historical proof behind it. It is equally likely that the Norman ruling caste, who were closely related to the Viking royal houses of Scandinavia, sought to re-establish the Viking power in England that had been thwarted by the Saxons following the end of the reign of Cnut (Canute). Hence the alliance that led to the Norwegian landing in the north led by Harald Hardrada, as a prelude to the Norman invasion in Sussex. The effort required of Godwinson in defeating the Norwegian army at Stamford Bridge meant that his forces were unable to repulse the Norman invasion.