Province

An otherwise good book I'm reviewing but has Castile as the "central province" of Spain, and the "annexing" Catalonia, Galicia, and Asturias over the centuries. He has Castile rising to prominence in the 15th century. I'm pretty sure that Castile was prominent under Alfonso X two hundred years before that.  

(He also has Pierre Menard trying to become Cervantes, when that is the initial approach that Menard rejects.)

There was never an annexation of Catalonia by Castile.  Catalonia was essentially part of the kingdom of Aragon, and the marriage of the Catholic monarchs Ferdinand and Isabel was the first main step of unifying Spain politically.

And of course Castile is not and never was a "province." That's a bit like calling England a province that annexed Wales and Scotland.

It is hard to state facts accurately.