AHC: Unify the Christian states in Spain in the 12th century

No gavelkind.

Contrary to what Crusader Kings II teach us, Gavelkind should be used only for Britain.

Anyway.

It's doable for Leon/Castille/Galicia as they were conceived being part of a same continuum, and even when kingship were distinguished, weren't really fully separated (hence the regular reunifications).
Navarre and Aragon is more tricky : contrary to what existed in North-Western Spain, you didn't really have a sense of continuity between Pyrenean Kingdoms (Aragon, Sobrarbe, Ribagorza, Pampelune) and while Sanche apparently tried to pull a Verdun by reserving the overkingship to Garcia, it was largely ignored by the local nobilities.

I suppose that a Navarrese victory at the Battle of Atapuerca could reinforce ties between Leon/Castille and Navarre, but maintain this situation up to 1100 is going to be really difficult, to say nothing about absorption of Pyrenean entities, and the traditional kingship separation would probably still play (as it did both in Leon/Castille and Navarre).

Eventually the Fitna in Al-Andalus provided more easily and wealthy targets for Christian expedition, than fighting each other (as well more ideological reasons for).

At best, you'd end with a royal supremacy over different basileus/regulus/bailius/kings by a Navarrese of Navarro-Castillan king/imperator by the mid and late XIth century but I really, really doubt it would be an actual unification or even that it would last up to the XIIth century for all entities concerned.

(Of course, County of Barcelona wouldn't really be, even technically, part of the whole thing. If something, a patchwork-esque behemoth would probably make it reinforcing ties with Foix or Toulouse, as Aragon did with Bearn IOTL, if not resuming sort of vassalage under French suzerainty if Navarre begins to be really threatening).
 
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