While I've discussed the origins of Andalusada in outline before, I haven't actually typed it out explicitly, and certainly not here. Now that it's hyperlinked, I have no excuse. So let's take this from the top. Andalusada starts in the year 1081.
In 1081, some politics comes up. We're not totally sure about what it was; there's some legends and such but it's not nearly as well-documented as we'd like. What matters is that Alfonso VI has been remarried to one Constance of Burgundy, who brings with her a lot of Cluniac ties, papal opposition, and personal drama. A fair number of people apparently got exiled because of them this, including one Rodrigo Díaz de Vivar, who leaves with no money and a fair number of retainers to feed.
With no loyalties owed to Alfonso, Díaz has to find a new employer. The first place he turns to is Barcelona, where he winters with the Counts. They hate each other. Passionately. Still unemployed at the end of the winter, Rodrigo is forced to look elsewhere to feed his cohorts.
This is the point of divergence. This is the point of departure. This is where Andalusada stops being IRL.