Dorrin 说:
Unless its changed recently there was a formula involving their factions number of walled fiefs versus your own factions number of walled fiefs, it also includes persuasion in somehow. If the option isn't there lock em up and get more land.
ah, thanks.
I recently started my kingdom, bringing only 3 castles, a town and the associated villages with me when leaving Ravenstern and declaring independence.
Unfortunately, my tenure as marshal of Ravenstern was a little too successful and so they also own basically all of Fierdsvein, making my task of reconquering Ravenstern in the name of the true Kingdom of Pendor a little more complicated

.
I have now been at war with them for about 80 days without them being willing to accept a truce. What was originally very much a defensive effort of throwing back siege after siege has now shifted to more general skirmishing (nice xp though - for some reason killing 50 knights and 100+ trash per siege with a bow helps!!). Whilst I originally was releasing lords so as to keep boosting relations and honour this meant I wasn't realling damaging their offensive capabilities.
I have now shifted to capturing lords to damage their military capabilities, but I really need to get some lords of my own!!
Oh well. Hopefully they will accept a truce if I keep on imprisoning their lords. I need a truce so as to be able to downsize my garrisons and do a few tournament runs to boost my coffers as after 80 days of being slightly budget-negative but pumping lots into a fledling CKO and KotRS stats my wallet is a little light. Hopefully I can also persuade some lords to jump over.
Anyway, here I am with my 'friends' so far. Plenty of space for more in comfy cells of Poinsbruck
edit: thanks for the details you added in your edit - v. helpful.