Also remember that wars outside the realm is allowed up to Absolute crown authority, you can attack weak lone states and claim them for yourself. If you take a title equal to your liege you can even secure your own independence!
Essentially this. If you swear fealty to a powerful and distant king, or Emperor even better, you can grow outside of the realm as usual, which in Iberia is a great because your surrounded by great opportunities every time there's a succession crisis in the big realms. The only possible problem you might have is that by swearing to the Kaiser or Basileos, he might realize that he's huge and powerful and a new little corner of his empire is surrounded by easily conquered heathens, so they might DOW the weak targets you intended for yourself and hence deny them to you.
Emperors are great because you can essentially grow to Kingdom level within the protection of the greater realm from outside invasions while being able to take potshots at neighbouring realms.
As to the mini AAR, right now... Diego I died, Diego II inherited. His brother, Luis, was made duke of Seville by Diego II but still rebelled in a succession crisis which thanks to the fact that Seville was recently conquered and wrong culture and religion didn't take much to put out. Right now the future King is my only son, Rodrigo, who's set to inherit my kingdom + Croatia and Jerusalem from his mother. Very vexingly though, I married him off to the daughter of the King of Castille Luis I, which was great because I would then be able to call on the Iberian ally. This King then died of old age, and his genius mastermind theologian son, and my son's brother-in-law inherited. I was looking forward to pushing my grandsons claim when he was born. Unluckily, someone killed Rodrigo's wife before she could produce a son, so I only have one granddaughter whose claim I might press. And then the King of Castille died sick in bed due to illness at age 30.
I'm thinking I'm going to push my granddaughter's claim to Castille while her cousin the current king is relegated to King of Leon alone. And then, when Galicia finally drifts into Castille and it becomes a titular title, I'll have her killed so my son inherits Castille from her. Yay!
There's been no growth in territories and Empuries remains Breton on account of a Second Crusade for Jerusalem; currently the Kingdom is de jure held by Queen Sofia the Just of Croatia, my lovely wife, though most of the territories are held by either the Fatimids or the Seljuks. The Crusade started during the reign of Diego I, and Diego II joined in the fun to try to get more counties to his wife which will later be inherited by his son. However, the Crusade lasted for 10 years and ended in white peace, and was truly a world war. The Seljuks in Persia reach the Meditteranean in Aleppo, and are also the same dynasty as the Sultans of Rum, plus all the sundry muslim realms who joined, against a laundry list of Kingdoms and Duchies. Terrain ended up being the main advantage though due to attrition and length between catholic reinforcements.
When the Crusade ended though, the Persians basically imploded due to a child king, and they're hovering at 97% decadence so I'm forseeing some nice expansion in the area thanks to rebelling dukes.
And a JIHAD was called for Andalusia by the Sunni Caliph against me. Again. Thankfully Europe came to my aid, and the Hospitallers where hired for some piety and 0 maintenance costs, plus some of my levies where able to crush the armies marching all along Africa as they didn't have enough boats to move the massive stacks, so I was able to intercept them with ship landings at 2 to 1 odds or better almost constantly.