Someone please tell me how pressing claims for other characters works

[Lannock]

This is pretty annoying.

I married my ruler's sister off to a character that had a weak claim to another duchy, gave him one of my counties then went to war on his behalf. I just spent about 9 years winning the land for him only for him to become independent, even the county I gave him has become part of his domain! How does this happen???

If giving them a county isn't enough, what exactly do I need to do to prevent them from becoming independent?

 

[perpetualmuse]

Are you a King? If you are pressing one of your Count's claim for a duchy, then you need to be a King or Emperor to be able to keep the person as a vassal since a Duke can't be a vassal of a Duke.

 

[Ness_Uno]

The targeted title needs to be under one of your De Jure titles. For instance, if you are King of Sicily and pushing a claim on the Duchy of Calabria.

OR the claimant needs to be a dynasty member. So in the case, if the claim is inheritable, you could press the claim of the child, assuming the marriage was matrilineal.

 

[perpetualmuse]

The targeted title needs to be under one of your De Jure titles. For instance, if you are King of Sicily and pushing a claim on the Duchy of Calabria.

OR the claimant needs to be a dynasty member. So in the case, if the claim is inheritable, you could press the claim of the child, assuming the marriage was matrilineal.

This is not true if the claimant is a vassal Count as the OP says was the case. I suspect that it's just because he/she is a Duke pressing someone else's claim on a duchy, which obviously prevents vassalization after the war is won.

 

[Lannock]

I'm only a duke myself so that explains why he's not my vassal anymore. Thanks, I understand now.

If I'm getting this right, I can still press a claim for another character for a county as Duke and they will remain my vassal, correct?

 

[perpetualmuse]

If I'm getting this right, I can still press a claim for another character for a county as Duke and they will remain my vassal, correct?

If the claimant is already your vassal, then yes. Otherwise the claimant has to either be of your dynasty, or the title you are trying to take must already be de jure part of your realm.

In your game, you just can't keep the guy as your vassal because he gains the duchy making him a Duke and of equal rank to you; equal ranked characters can't be a vassal of each other.

 

[Gnorrosch]

So, just to get this right: If I (as a king) invite someone to my court, grant them a barony and then wage war for their duchy, they become my vassal, because (as a baron) they are my de jure vassal?

 

[perpetualmuse]

So, just to get this right: If I (as a king) invite someone to my court, grant them a barony and then wage war for their duchy, they become my vassal, because (as a baron) they are my de jure vassal?

Yes, the Baron would become your Duke vassal after the war was won and keep the barony too. You specifically asked about de jure vassals, but it doesn't matter whether or not the claimant is your de jure vassal or a non-dejure vassal, just that they are a vassal before the war.