Why would you feel the need to do this? It does you no good, and it does the game no good. All it does is drive players away.
80% of the time, we are attacked first by a group that was good on an RP server. It becomes tiresome having to constantly show these people they are not on an RP server.
I think you are right when considering one large aggressive guild declaring war on another large aggressive guild. If, however, you are a large aggressive guild declaring war on a small peaceful guild, you are not really taking any risk.
Are you honestly saying a large aggressive guild should not be able to crush or subjugate a small peaceful guild that is sucking up local resources? What if they are acting as a staging and resupply point for a more aggressive guild that they are allied with? If they are not willing to pay tribute or join the war party then they need to move their base. They can have fun somewhere else in the game. It is a big map after all.
The game is called "Life is Feudal" not "Life is Tribal".
Google "feudal system" if you are curious what that means.