Installed a few mods (expanded ambitions; less blobby HRE; religious wars only declarable on neighbours or crusade targets) and restarted as the King of Castille. In 1066, historically, the death of Fernando the Great meant a Gavelkind split into Galicia, Leon and Castille by his three sons. Almost immediately, the King of Galicia seemed to suffer some sort of accident and become incapable, but before I could move in, the King of Leon assassinated me. Of course, being my brother, I was now playing as my assassin, and the incapable one soon died naturally to restore a relatively powerful Castille/Leon/Galicia/whatever.
I spent the next twenty years aggressively expanding into Muslim Spain, looking to cut off the Kingdoms of Aragon and Navarra, and the Duchy of Barcelona, from expansion. Soon I had Toledo, Valencia and couple of other holdings, which I quickly redistributed to various courtiers - high stewardship, no ambition trait, and often looking for Content or Shy. King Alfonso was known as the Great when he passed away after nearly thirty years of rule. His only flaw was an extramarital liaison that produced two bastard sons, but he decisively denounced them and granted them bishoprics before his death, taking them out of succession entirely.
His son, Alfonso (VIII, I think), had pretty good stats, and got involved in a very difficult war against the Emirate of Beja, the biggest Muslim threat remaining in Iberia. Since waiting for them to declare war means a huge waste of time, I declared early to use a CB and then needed to disband and reform my levies several times, as well as three mercenary armies that broke their backs on the Muslim wave, finally only winning with the help of my blood-related kings in Navarra and Aragon. But he died of mysterious causes (may well have been an undetected assassination). Now his only son, 15 years old, faces a powerful uncle, the Duke of Toledo, who looks almost certain to rebel, as well as several other vassals that are clearly waiting for the right moment. After the recent war I have neither cash nor troops to keep everything in order, so things may well implode from here on in.
I should mention that the religious war mod is a nice temporary fix for the France issue - since they don't border any Iberian muslims at game start they have no good CB, and thus have not set one foot into Spain. Now I'm trying to figure out how I can get Pope to call crusades (if you can do that at all).
