Actually "The Kings Demons" is even more complete twaddle than this is, as AFAIK Magna Carta meant bugger all at the time, it was later centuries who ASSIGNED it a lot more value than it actually had because it suited them.
And given the main character here is called Supreme, I can imagine that the rest of the story might actually have been derived from the wordplay in making his new self "Supremacist", a word with singularly unpleasant connotations.
Plus I'd say the Confederacy winning really IS a background art shot, effectively, as the story has more to do with time, consequences and the implications of "Wibbly-wobbly timey-wimey stuff" (Thank you Stephen Moffatt) on a team which culls it's members from past, present AND future, and so have an intruigingly disjointed view on cause and effect (Whenever they show up in Moores run even their casual comments make my head hurt)