*Cough* You do know I am French UE, don't you? *Cough*
But your explanation would require the use of Temporal devices in order to know William the Conqueror would conquer England eleven centuries later.
Therefore, France must master the field of Temporal Studies, at least to a certain extent. Either that, or France would hate to see another country conquering England, as this is their privilege. (Or rather, *attempting* to do so that is.
)
Your own hypothetis Growltigger also implies the use of some Temporal device, comforting one of the possibilities. Then you may want to ask why France did not use its Temporal knowledge during other battles, for such an asset would have meant victory. It was, obviously, to keep this secret... erh secret. *Grumbles, that explanation is really lame. But it will have to do*