Well, sorry. The only logical way to explain your move is that you wanted to reduce your battlefront and be covered for if this war failed. And maybe you wanted to piss of/copy darka for having a treaty with Talerium but you know, none of that is very risky.
Of course maybe none of these motives played in your decision but then I wonder which ones did..
Guys, its seriously the cookies...
In all seriousness though, I am amazed at how little people don't understand this situation or can see it from multiple viewpoints. Talerium and Darka have had a border treaty for years and years. Eston and Coria had the exact same border treaty BEFORE this war ever began. Eston's agreement with Coria was only to return to pre-war relations between our two realms.
By doing so, Eston secures their border, while forcing Coria out of the war. Eston is not to blame for Coria rejoining the war effort. (hi Hammarsett...) When that treaty was first signed, the northern alliance made a great gain in the war, and should have used it to start winning, but the only thing I saw was complaints about not being able to attack where they wanted to, and so the war stalled only because the northern alliance couldn't decide to work together.
Oh, and yes, lots of bribes of cookies.