Yes, there were occasions when the upper most echelon of royalty and the most powerful of dukes were able to marry within a royal or great house within a neighboring court or a court along an important trade route. But, really most royal marriage, at least for the first 100 years from 1066 onwards, was domestic.
Throughout the period covered in CK, marriage partners tended to be of the domestic nobility or directly neighboring realm. A king was more likely to marry the daughter of a powerful duke then he was a neighboring princess. Likewise, that same king was most likely to marry his heir and other children to his own powerful vassals in an attempt to bind them to him through familial bonds. Exceptions did exist of course, such as Alfonso VI of Leon’s marriage strategy to attract cross-Pyrenees alliances by marrying French heiresses. Additionally, Henry I of England married his daughter (and future heir) Matilda to the Holy Roman Emperor in an attempt to build relations with Germany to diplomatically out-flank France. And there was a Russian princess in the Scottish court in the mid-11th century! - Though I haven't fully vetted the circumstance behind that.
Yet, most Norman and Plantagenet rulers married domestically, or married into neighboring countries building diplomatic relations.
- William the Conqueror married Matilda of Flanders, neighboring realm
- Henry I of England married Matilda of Scotland, neighboring realm
- Henry’s heir Empress Matilda married Geoffrey of Anjou, neighboring realm. Matilda had first married the Holy Roman Emperor, one realm away from France.
- Henry II married Eleanor of Aquitaine, one realm away from Normandy
- Richard the Lion-heart married Berengaria of Navarre (or he married her brother Sancho!) Navarre was an important neighbor to Richard’s Aquitaine.
- John married Isabella, Countess of Angouleme (an important county and vassal of Aquitaine), and John had a favorite but illegitimate daughter
- Joan married to Llywelyn, Prince of Wales and Gwynedd.
- Henry III married Eleanor of Provence, an important county next to Aquitaine
What I propose is for the AI to take into account the kingdom and its neighbors, and value potential marriage partners based on their prestige (prestige reckoned partially in their social ranking- royal family, ducal family, comitial family, but also on their nearness to inheriting).
It's a preference, but if it seems to complicated then its not something Ill get my panties in a bunch over
