When I write, I must get into the heads of my characters. If I refer to actual figures from history, I must study their character and have them react to my fictional setting in a natural way. Thus, If I am to write a fictional history where the original inhabitants of this land conquered Europe, I would need to study the nature of the participants of the story and apply my what-if scenario then predict how they would react to that.
I would also have to decide on a point of view. As we all know, actual history can look very different depending on who is telling the story. Unfortunately, the victors get to write the history books, so we have much less information from the point of view of the losing side.
Any comments will be appreciated. What do you think of the premise and how do you think it would evolve? Let me know all of your thoughts.