Darka and BoM raided Coria back when Eston and Coria were "friends" as well.
That is why Eston will never be a Great Power, no matter how many regions or nobles it has. It can't stand up for itself, and gives passage rights to their "friends" so that they can raid and loot Eston's other "friends".
Eston is basically the battered wife of the Northern Alliance.
