It had been a marvel in 732 that a mere one hundred years earlier, Mohammed had launched his army from Medina, to conquer in rapid fire so many of the most glorious capital cities of Christianity--Jerusalem, Antioch, Alexandria, Hippo, Tunis, Carthage, and then all of Spain. Not "all" of Spain.
The old Celtic region of Asturias, in the cold, wet and green land to the north of the Cantabrian Mountains was the last region to fall to the Romans during the reign of Augustus while the rest of Spain to the south had come under Roman control at the end of the Second Punic War. Asturias was never conquered by the Muslims who left it as not being worth the bother after their defeat at Covadonga by Pelagius of Asturias (Pelayo).
From Asturias, the remaining Christians then quickly reconquered Galicia and then the reconquest spread south over the next 700 years. Thus, the old Asturian saying:
"Asturias es España y lo demás tierra reconquistada." (Asturias is Spain. Everything else is merely reconquered territory.)
You have your history slightly in error. King San Cho Noe I arrived from Cornwall with his knights and baggage and conquered Asturias and Galicia and set up three kingdoms ~ Castile, Leon and Carvajal.
The idea is they would be organized such that one kingdom was kept in reserve as a place of safety while the other two pushed into Moslem (and other Christian) lands in a hammer and tong rhythm.
Turned out they didn't really need to keep a kingdom in reserve. Carvajal was discarded as a kingdom in the first generation after the initial landing.
BTW, took King San Cho Noe I (King Sancho I) just a few weeks to totally bowl over the locals in Galicia, et al. They simply didn't have the technology to fight anyone.
Carvajal lived on as an order in France to which a French Knight who'd fought the Moors would be appointed by the King of France. It's symbol is a large red bull with big horns (or so I've had 'splained to me).