'They can conquer any province bordering one of their own for 50 Piety (vassalizing the current count if possible)'
I'm not sure I like this. It's going to make starting out as small Muslim counts SUCK, when all of the larger Muslim states around you can just conquer you whenever they feel like it.
Oh, it sucks much worse than that: Your liege doesn't gain any tyranny for revoking your title under certain circumstances. So you have to grow quickly or die.
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Protip on handing out count titles after a war on foreign, infidel soil: That land you just conquered will be useless to you for a long time, but may be more developed than your land. So in the future, the land you just conquered will be better than your current land, but for now it is just sapping your tax income.
Whatever shall you do?
Give land to celebate characters in your realm (you can give land to any male in your realm, including the courtiers of your vassals). When they die, it reverts to you. Of course, celebate characters can still have children in Crusader Kings, albet rarely, and you won't inherit the lands of counts with children. But it will work most of the time.
A more risky alternative is to marry your old male courtiers to female courtier past childbearing age, then give the male courtier land. But your new count might just decide to kill his wife and marry someone younger, or the wife might just die of natural causes. So it is risky. And DON'T marry your male courtier to any female with fertility-modifying traits, because ANY fertility modifying trait allows a woman to give birth after childbearing age.
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Fun thing to do when you hold all the territory in your realm: Change laws. Your new vassals will be coming after the law change, so they will mostly accept whatever you change the laws to as the status quo they have always lived with. On a related note, the best time to raise tax/levy levels for the respective vassal types (castle, town, temple) is when you have no vassals of the respective type.
Pffff, what. My wife was plotting to kill me at +46 relations to me. What the hell. Why? Why would you do that?
One theory is that the high frequency of kill plots are simply due to a lack of ambitions for most characters. Your wife is only plotting to kill you because she has nothing else worth striving for in her life. Some of the mods try to address this by adding more ambitions.
Or maybe she just feels that she can do better?