Yeah sort of. Brumund is a small kingdom compromised of a collection of small towns and villages and just the capital itself. Any of the local major powers could in theory roll them, but that won't happen due to the many treaties already in place between Brumund, Dwargon, Ingracia, and Ruberion with Ingracia being a neighbor kingdom to Brumund and home to the Adventurer's Guild HQ. The benefit of the treaty actually DOES benefit Tempest more since it means a major non-neutral human kingdom acknowledges them as a legitimate nation and conflict with the Eastern Empire would have been unavoidable no matter what since they'd have to go via the forest and thus clashing directly or going via Dwargon and triggering their support treaty there. Rimuru still did get played, but his only real loss was not asking for a bigger kick-back. As for their support, I can't detail due to spoilers and the sheer fucking awesomeness of it all and I really can't wait for that shit to go down...which won't be in manga form til probably March of next year at the likely earliest.