Most regions on Spain had independent laws up to ~1700. While they belonged to the same Kingdom, they kept some independence. That level of independence was erased after a secession war that started on 1700, and ended with some decrees (Nueva Planta decrees, 1716 for Catalonia) that removed some "furs" and constitutions (not only in Catalonia, but everybody that supported the Hamburg's successor). And this was done using the term "derecho de conquista" (right of conquest).
Since then. I think that the source of conflict is that, for multiple reasons, catalans wanted to be part of a bigger political reality, but in "their" terms. And Spain, as a centralized system, didn't like that, doesn't like that and will not like that. To Spain, Catalonia is a property, why would they let it go? After all, it's their right (of conquest) to keep it.
It’s a bit misleading to say that Catalonia (along with other regions) was “essentially annexed” by Spain three centuries ago when it had been already be part of Spain for two centuries already. Since the very creation of the Kingdom of Spain. (It’s true that it tried to secede in 1640-1652 but the result was the loss of its northern territories to France. By the way, Napoleon would actually annex Catalonia to France later.)
Anyway, they level of independence that Catalonia has had in the last decades is much higher that before that “annexion”.
> Anyway, they level of independence that Catalonia has had in the last decades is much higher that before that “annexion”.
I am sorry to say, but this is the misleading part. You can't compare the situation hundreds of years ago with today's standards. Politically, Catalonia has less level of independence than 300 years ago. After all it had its own political institutions, courts, laws and coinage of money; all of them separated from the Kingdom of Castile.
The annex I was referring to was political, economical, legal and monetary unification after Catalonia defended a different candidate for the crown. And this is the level of autonomy that some Catalans wanted to regain.
Since then. I think that the source of conflict is that, for multiple reasons, catalans wanted to be part of a bigger political reality, but in "their" terms. And Spain, as a centralized system, didn't like that, doesn't like that and will not like that. To Spain, Catalonia is a property, why would they let it go? After all, it's their right (of conquest) to keep it.