Simple question really.
What if the Iberian Union never collapsed?
How would the peninusla develop over the several hundred years between its end in OTL and today of it the unification had remained in place?
Nah but seriously a combination of Spain and Portugal would've been a terrifying power, even into the later centuries. The decline of Spain could've been relatively slower with the assistance of Portugal, and they could've been a power to rival Great Britain and France into the 1700's.