Hrm. One way to do it would be similar to Germany. In Germany, you had 6-10 tribal duchies (they splintered over time), which all were pretty independant and had a stron national identity. Especially the Saxons and the Franks often clashed. Yet, the German Kingdom stayed together, something that was respected by all the Dukes. And that wasnt due to loyality to the King - uprisings against the King were a normality. However, the aim of each of those revolts was to install the revolt leader as new King. Basically,e very Duke tried to use his Duchy as a base to become the next King, and hence all Dukes had a stake in the continuinge xistance of the Kingdom.
Now, maybe, something like that happens in Asturias, too. It would require that all partial realms are merely Duchies, with an elected King leading them, of course, because elsewise there would be no sense in going for a higher title (as it wouldnt be higher), but, yes, I think the basic dynamics ar etrasplantable.