Prior to 1484
The Turei Alliance is a space-faring military and economic confederacy of species native to the Gradin Belt. Founded in 1484 when the Turei united with their neighbors to defeat the Vaadwaur, the Alliance has existed for nearly a millennia through a mutual interest in control over the Underspace. In 2399, the Federation formed a soft alliance with the Turei Alliance, permitting Starfleet limited access to the Underspace.
For hundreds of years, the Vaadwaur maintained a tight grip on the Gradin Belt through control of Underspace, a set of subspace corridors throughout and beyond the Gradin Belt that provided a major tactical advantage over other regional powers. When the Turei became warp capable in 1300, the Vaadwaur immediately tried to subjugate them. The Turei resisted, and the Vaadwaur responded by levelling several Turei colonies. Rather than break their resistance though, this only strengthened the resolve of the Turei. Over the next hundred and fifty years, the Turei sought out neighbours who, under the banner of the Turei Alliance, eventually pushed the Vaadwaur back. In 1484, the Alliance's campaign culminated in an orbital bombardment of the Vaadwaur homeworld, retribution deemed fitting for the crimes the Vaadwaur had committed against their people.
Nearly a thousand years since the defeat of the Vaadwaur, the Turei Alliance is currently a full-fledged interstellar power with a burgeoning economy, an impressive fleet of ships, hundreds of cubic light-years of territory, and an overly-complicated bureaucracy that manages their antiquated society and form of government. They are wary of intrusions into their territory and challenge any ship found or attempting to use the Underspace, but otherwise maintain fairly peaceful relations with their neighbours, although they are a naturally wary and methodical species, mired in protocol.
In 2376, the USS Voyager discovered a Vaadwaur battalion that had survived in stasis pods on their homeworld. While the Turei destroyed a large number of the surviving vessels, fifty-three managed to flee into the Underspace. Since then, the Turei have renewed their mandate to exterminate the Vaadwaur, expanding their patrols and sending out expeditions through the Underspace to search for any signs of the return of the Vaadwaur, although this has become increasingly-forgotten and less highly prioritised as the decades have passed on.
Even though some Turei hold the Federation responsible for reviving the Vaadwaur, their fear of the Vaadwaur and other mercenary threats led the Alliance to propose a pact with the Federation (and, therefore, an invitation to Starfleet) against the Vaadwaur. This treaty allows the Federation to use the Underspace in accordance with maps and support from the Turei, and to operate with Turei support in the Gradin Belt.