So, I've read that Harold Godwinson's biggest mistake at the Battle of Hastings, was to engage Norman troops without all his own soldiers.
I've also heard it said that there were a couple of reasons that Harold, though a decent (and intelligent) commander, chose to engage Duke William when he did.
Reason 1: The Normans, who were notorious for being brutal raiders, if I remember right, were landing on Harold's old personal domain. He really hated that because, HE was KING, and how dare they touch his family's ancestral lands!
Reason 2: Supposedly, Harold was quite a pious ruler, and was disturbed when he learned that the Pope gave a Papal flag to the Normans, and was apparently horrified that the Pope believed William's story about Harold swearing loyalty to him.
So what if, in his first act as king, Harold sends word to the Pope that he will enact several religious reforms, to make the Pope less desirous to support the Normans?
What if, he also takes a moment to think, before rushing off to fight Duke William, and gathers as many troops as he can?
What effect does that have on the Norman Conquest?