Hi Tyr!
Your question is good comrade!
The fact is REgnum still Beta stage is... the forts and castles right now must be captured for testing purposes only (and some honor things
)
Like Ar saids, all this structures make the holekey to the realms, so, if the 3 structures of any kingdom fall at the same time, the door will be open and the invasion came.
The only place to be safe for pvp will be passing trought the first door, in the initiation zone.
This dsn´t work right now, but taking the structures give hints over if they´re working well or bugged (like some doors in forts, or flags... )
So, hope this be what u looking with this question.
Have a good new year!