How to defend a vassal?

[openyun]

I have a vassal and it was being spied and attacked from time to time... how do I defend it?

[Angela]

Vassals can be taken over in case they are located outside your exclusive zone, other players can fight their army and fortress inside and they will receive the vassal territory upon successful siege. You can't participate in the battle and defend the vassal. You can take over the vassal again upon successful siege attack or annex the vassal (which will make it annexed province) if it shares a common border with other annexed province or the capital.