Double-Blind Challenge: Castilian-Navarrese-Aragonese Union!

The challenge, should you accept it, is to form a union of these three crowns with a POD no earlier than 1460.

Bonus points if this blob somehow becomes a dominant world power sometime after 1500. And if you want an extra-harder challenge, try getting Portugal into the mix too! :D
 
At least to some degree it would 'merely' be a question of trimming the royal families at certain points, either by disease or by war, so the crowns end at two persons from said realms, thats allready married previously ... kinda like the Slavic Empire sitting on the Polish, Hungarian and Bohemian thrones, with strong family ties to Grand Duchy of Lithuania, which the Empire on again/off again de facto ruled over
 
The challenge, should you accept it, is to form a union of these three crowns with a POD no earlier than 1460.

Bonus points if this blob somehow becomes a dominant world power sometime after 1500. And if you want an extra-harder challenge, try getting Portugal into the mix too! :D
Have Blanche II have a child with Henry IV of Castile and have both Charles Prince of Viana and John of Aragon die early and have Ferdinand of Aragon not born as well.
 
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