The nation is a kingdom with the throne jointly held by the king and queen, who are also the duke of Mimbre and the duchess of Asturia. Due to the delicate political balance, the king and queen give up their given names to rule as Korodullin and Mayaserana, the names of the first Arendish monarchs, in order to promote greater unity. There has also been an excessive degree of inbreeding to preserve the familial ties. Though technically these two duchies are equals, Mimbre treats Asturia as a vassal state until the end of The Belgariad.
The major reason behind the discontent between the supposedly equal Duchies was a refusal by the Mimbrates to recognize Asturian titles after the formal unification. The conflict arose over the requirement that the Asurians swear an oath to the new King and their previous oath to the original Duke of Asturia. As the Queens of Arendia - in the closely interbred Royal line - were direct decedents of the Duke, then the Asturians' oath was still very much in force. The current Queen of Arendia (in her capacity as the Duchess of Asturia) released all Asturians from the oath, at which point they swore their oath of allegiance to the King of Arendia (but not to the Duke of Mimbre though technically he is the same person as the King). With this issue solved, it is presumed that all Asturian titles were formally recognized. Indeed Asturians such as Lelldorin then freely started to throw themselves into formally 'Mimbrate only' internal conflicts and were welcomed 'to the party' just as quickly.
Arendish society is feudal, built on the institution of serfdom. Rival lords seem to be continually skirmishing, and when they are not, they are holding tournaments during which they hone the skills used for skirmishing. Arends are typically viewed as not too bright and sometimes overly proud, though they are universally hailed as being loyal and brave. Unlike the gods of some other peoples, Chaldan does not intervene much in human affairs.
Many among the Asturian nobility are renowned archers. Serfs are used to provide support.
† Erat had strong ties with Wacune, but couldn't aid it against the Asturians, though they did defend their own land, with Polgara controlling the battles and communicating with her generals with her mind.
Mimbrate forces typically fight as heavy cavalry, with armored knights riding armored warhorses and 'men at arms' supporting them, often with pikes and siege engines. Serfs provide support, mostly as cannon fodder in attacks.