Experienced and ruthless leader, not a king but a duke, led a modern army with innovative tactics, claimed Edward had promised him the throne, backed by the Pope and several allies
Death of Edward the Confessor led to a succession crisis with four main claimants: Harold Godwinson, Edgar Atheling, Harald Hardrada, and William of Normandy
William of Normandy had some claim, promised support by Harold, gathered an invasion force with allies, poised to launch an invasion of the south coast