What are the requirements for a king to usurp a duchy in another kingdom?

[Sleight of Hand]

As king of Lotharingia within the HRE, I managed to conquer Burgundy for my cousin (he had a claim thru his mother) whilst it was independent during a war against France. He then accepted my invitation to be his vassal, and everything seemed fine for a while. He then got into a war with another duchy within the HRE; I wasn't really paying attention (I didn't really care who won as they were both members of my family, cousins from different branches) but then all of a sudden the king of France usurped the duchy of Burgundy and all its counties, which then went back into France.

Under what circumstances can this happen? Burgundy is a de jure part of France, but at this point it was part of Lotharingia within the HRE, and the duke was my cousin. Wouldn't the king of France have to declare war on the Emperor and take Burgundy in a proper claim war?

I can provide a save game if needed. This is just with vanilla 1.07b.

 

[Dracko81]

Internal faction, where the duke surrenders to the demands of a count to have a claimant take over the duchy title.

 

[Comradebot]

Possible a faction presented an ultimatum.

 

[Mutineer]

he can usurp duchy normally if 1/2 or more counties in ducy still in his kingdom.

 

[tuareg109]

Hmmm...so when a Faction presents its ultimatum and the victim--for lack of a better word--accepts, and something happens like in OP's case, why doesn't it ask the victims liege whether he will declare war?
It doesn't make sense that if a king has a duke-level vassal and that guy abdicates to somebody who swears fealty to another king, that he'll just say, "Oh, well, okay, nothing I can do about it." He'd say, "WHAT THE HELL!!!" and he'd go to war for control of the duchy (probably). I'm no expert on feudalism and medieval government, but a think a liege should be able to protect his vassal from Factions.

 

[Dracko81]

Yes its been discussed a few times, but I have not seen a dev comment on whether or not it was being looked at.

 

[Tokie]

If I remembered correctly, a few patches ago I was able to revoke duchies under internal conflict so I can end their war prematurely. Did they change this recently? Because I really wanted to change my succession law, and someone is always rebelling against their liege in a stalemate.

 

[Dracko81]

If I remembered correctly, a few patches ago I was able to revoke duchies under internal conflict so I can end their war prematurely. Did they change this recently? Because I really wanted to change my succession law, and someone is always rebelling against their liege in a stalemate.

That was an exploit/bug, you should not be able to revoke or transfer titles currently affected in a war.

 

[Tokie]

That was an exploit/bug, you should not be able to revoke or transfer titles currently affected in a war.

Then I believe when a count rebels against a duke, the count should not be labelled as my direct vassal. The "vassals not fighting each other" condition to change succession laws requires high degree of luck in a large empire.

As the ultimate liege lord, I should be able to do something right?

 

[Dracko81]

Then I believe when a count rebels against a duke, the count should not be labelled as my direct vassal. The "vassals not fighting each other" condition to change succession laws requires high degree of luck in a large empire.

As the ultimate liege lord, I should be able to do something right?

The key word here is "large", it is not so much an issue with small empires, but large empires. So yes it should be hard to change succession laws with large empires.

The liege being able to become involved with vassal wars has also been spoken about many times and never directly responded to by dev's - so far as I know.

I am sure they know about peoples concerns and are probably looking at ways to fix them. The issue with changing mechanics is that one minor change opens up ways to abuse the mechanic, so some things like not getting involved in vassals may never be changed.