Well, first of all the reason for doing this is quite easy. We want a conflict. The best way to make people angry is to attack someone, especially someone that will whine about it. Then, who can we attack? Either our allies in the east, or allies in the west or that huge and rich neutral realm down south. It is indeed problematic that you are already in a war, and thats why we arent really attacking you and declaring war, but merely doing some looting.
For the IG purpose of the lootings (our treasure hunt), I do like it alot. The whole idea is to take gold and tell the world that we can do it because the whole world fear us and cant do anything about it. This is good for two reasons: Its awesome, and it gives a good chance of making surrounding realms angry at us. Which idea could ever be better than this?
As for being meta-gaming I would be happy to see you develop it, since I see each of these reasons being quite IG. The only ooc reasoning here has been to not make war on Nothoi, so as to not make the war too lopsided.
As for the rumor that Thalmarkin was going to attack Rio, I have also heard it ooc, and I have really no idea where it came from... Certainly not us at least, and definitely not IG.
