dont understand a game rule

[Bruccy]

how can it be dishonourable to start a subjugate war immediately after the war target tried to steal a dutchy , makes no sense

[brownacs]

It sounds like you had a truce. You can see them on your character's page with your alliances (might have to expand it).

[Bruccy]

truce or not this guy deserves to feel my wrath he started it lol , it was just luck i was able to defend myself =)

[Deusmodeus]

Your allowed to attack a nation if they attacked you and you won (one way truce)
Otherwise your either allied, hindered, or recently attacked them.

[Bruccy]

i also do not understand why my realm will lose land after a subjugated vassal dies

[Deusmodeus]

Originally posted by Bruccy:

i also do not understand why my realm will lose land after a subjugated vassal dies

The Heir of the subjugated land is a landed lord who is not part of your realm.

It sounds like:
1) Your laws don't prevent titles from leaving your realm
2) After conquering the land, you did not check to see if the heir would result in the land staying inside your realm

I highly recommend forcing civil wars and purging old nobility. Better to pass the land to your own family or to smaller newer noble families.