Apparently you have to siege every holding in each county. This could take a while... I've extorted Weimar from my neighbours, I'll have to wait 10 years of cease fire for the next county I want to take from them. Apparently you can only claim land for which you used the CB or something, I'd like to get multiple counties in one go...
Another thing, I've lost a county. While I was busy getting Weimar back from Meissen, the emperor reinstated the duchy of Braunschweig. I don't know why, maybe he's insane, maybe he got paid for it. Anyway, when the count of Friesland (and Braunschweig) died, his lands were distributed among his heirs. From what I can reconstruct (not paying attention, remember... not that there was a popup of any kind, it just happened) one of my vassals was one of his heirs, so he inherited Braunschweig. Because he was the lord of Oldenburg this means he now owns two counties in the de jure duchy of Braunschweig, so he claimed the title. This made him a duke, and since dukes can't be vassals of other dukes, he devassalised (is that even a word?). Even worse, since he is the duke of Braunschweig, he now has a CB on almost all my territory.
This sucks. Well, at least now I know why the
advanced small start guide says I should imprison all my vassals right at the start. Sigh. Oh well, perhaps not all is lost, I might figure out a way to get a CB on him. I might just as well restart, since I'm only two years in the game.