Much is said about Harold rushing to meet William at Hastings, and in hindsight should have waited in London to bring a fuller force down. In my understanding he spent around 10-14 days in London after leaving York some 5 days after Stamford Bridge. Surely this was ample time for the Northumbrian Earls and their huscarls to join him? Could this be seen as trecherous, why else would they take so long?
I understand that they arrived after the battle, and played a role in the defence of London in Williams assault from the south, before essentially deserting, after william had ridden west all around the thames, laying waste to the south, before turning north and approaching London from the north. Again, can this be viewed as trecherous? That William kept them in place as the Northern Earls post conquest, would lead me to believe so....
It is rather easy to suppose that Morcar and Edwin were hostile to Harold Godwinson and deliberately left his army weaker than it otherwise could have been. However, this is an incomplete view of the situation in Northumbria at the time. The Norwegians had been defeated by Harold's army, but not before he had in turn defeated both of the northern earls. While the specific details and casualties of this battle are not quite fully understood, it is certainly not a stretch to imagine that Morcar and Edwin were not in top fighting shape at this time.
Now of course that does not preclude some element of treachery between the English earls. Morcar and Edwin were of course powerful landowners and it's likely there were some tensions between the powerful lords. But theres little evidence of direct conflict between them all. Indeed Morcar and Edwin did not contest Harold's coronation.
The argument of collusion with the Norman's however is totally unconvincing. In 1068 Morcar and Edwin started a rebellion against Norman rule that resulted in their subsequent defeat. Edwin died during the revolt and Morcar was defeated and stripped of his titles. They did hold onto their holdings in the immediate aftermath of Hastongs but they were neither secure nor long live in their positions.
Whether these noble earl brothers were at Stamford Bridge or even Hastings is a moot point, it is of course very possible that they were with their own housecarls but no sources, Norman or English, confirm this. Had they been, sources surely would have recorded it. Certainly someone with the authority and notoriety led fresh troops with panicking, retreating fyrdsmen men at the Malfosse (the English 'last stand'? Or confusion with an event during the battle? Sources differ). Earl Waltheof isn't recorded much in 1066 either?
The generally accepted belief is that these young and inexperienced brothers and Earls (Edwin of Mercia; Morcar of Northumbria) had only their own interests at heart and so betrayed not only their new brother-in-law King Harold (who had agreed to marry their sister in return for their armed support) by failing to show up at Santlache on October 14th, but also the nominal young king Edgar afterwards by fleeing London intially as William approached, after his victory.
But is it as straight-forward as this?
A first cousin of theirs, Abbot Leofric of Peterborough, was actually present at the battle at Santlache, so their family's involvement in Harold's cause was taken seriously, despite the traditional antagonism between the Godwinsons and Edwin & Morcar- and their renegade father, Earl Aelfgar, before them. They also had a vested interest in seeing Harold succeed- their own sister, the new queen, was pregnant with their king's child!
In all fairness, they had resisted the ousted former Northumbrian earl Tostig Godwinson's raids in Lindsey earlier that year, forcing him to abandon his attacks and seek refuge in Scotland with King Malcolm III, his 'sworn brother'. This could be seen to be more because of their hatred/fear of the ousted Tostig's vengeful wrath than of loyalty to Harold.
But then they did block the route to York from the Norse invasion army under King Harald Haardrada at Fulford Gate, lost that brutal pitched battle, fled the field and were in no position to fight on with such devastated forces.
They did not submit to William immediately after Oct 14th, but rallied around Edgar briefly. It was only after the witan and churchmen chose to submit to the duke that the young Earls joined them at Berkhamstead. Then fled the city- presumably northwards to protect their sister and unborn child.
In a few short years, during which they don't appear to have collaborated with William's new regime, did they escape from his gaols and raise revolt against him.