The Rish-Natal Combine
On the far rimward side of the Vast exists the Rish-Natal Combine.
First encountered by the Klingons in 2198, the Rish-Natal have demonstrated technological superiority at least 50 years ahead of the major powers of the Alpha and Beta Quadrants. They previously claimed the Vast as part of their territory, peppering the borders of it with defensive space stations every 50 light years, for a total of 8 stations along the coreward border. While they never launched a strike corewards, they strenuously resisted any foreign military excursions into their territory, ably defeating both the Klingons and Gorn on a few occasions.
In 2297, the Rish-Natal announced that they had withdrawn to the other side of the Vast, and informed the local powers that these gutted stations were available for occupation. They would also permit exploration of the Vast and surrounding regions they had previously claimed on the coreward side of the Vast. However, they did so with a caveat — all governments must abide by something that amounts to Starfleet’s Prime Directive. No interfence with pre-warp civilizations would be permitted.
Since then, they have not responded to any contact attempts, though their ships have occasionally been seen.
No one on the coreward side of the Vast has ever seen a Rish-Natal.