It all began with the death of Edward the Confessor, in January 1066. The Bayeux tapestry depicts Edward on his deathbed, offering the English crown to Harold, and this event is reflected in most of the chronicles of the time.
Edward's corpse was eventually borne in state to his own new cathedral church at Westminster, and the tapestry shows Harold there, being offered the crown by the magnates of England, among whom must have been Edwin and Morcar.
Harold was crowned at Westminster Abbey by Archbishop Stigand of Canterbury and Archbishop Ealdred of York. It is significant that only the former is depicted (and actually named) on the Bayeux tapestry, as his appointment had never been recognised by the Pope, allowing the Norman propaganda machine to portray Harold's coronation as illegal.
On the tapestry, the members of the congregation shown as witnessing the event are facing Harold, but their eyes are turned towards Halley's Comet, which is depicted in the sky as a portent of the doom to come. Harold is seen receiving news of the Comet with fear in his eyes. These bad omens for Harold were important to William of Normandy, who was set on claiming the English crown for himself - omens as important as the 'promise' of 1051 and the 'oath' of 1064. This was because, despite his pre-eminent position, he required the active co-operation of his nobles for the great venture he was planning - the venture to invade England and become the English king.
William could not just demand support from his nobles, he had to convince them of his case. He needed to show his followers that his claim was a lawful one, and that he had God on his side. So when he decided on invasion, he took elaborate measures to ensure he had strong support, and even sent an envoy to the Pope asking for his blessing.
William did not move immediately. He only began plans for an invasion after Tostig arrived in neighbouring Flanders, looking for support against Harold in a projected invasion of...