Suah'Dron was a star system located in the Regula Badlands. Like most of the Regula Badlands, this system contained radioactive nebulae, including a tachyon nebula. In 2377, the Borg picked the Suah'Dron system as the location to construct a transwarp portal, linked to the Bora system in the Delta Quadrant. Once the portal was complete, the Borg quickly fortified the system and moved to assimilate surrounding areas.
However, Starfleet was able to discover that the Suah'Dron system contained the portal (from studying the assimilated Nebula-class USS Douglass), and a Federation counter-attack led by the USS Enterprise-E was able to capture the transwarp portal and fortified the system. Starfleet then used the portal to travel to the Delta Quadrant and launch a series of operations against the Borg there.
Shortly before the Federation task force returned home, the Borg Queen (who had joined the attacking Borg fleet) led an attack on the Suah'Dron system, attempting to retake the portal. Starfleet opted to destroy the portal rather than let it fall back into Borg hands. This action severed the link between the Suah'Dron Borg and the majority remaining in the Delta Quadrant, and also stranded a small fleet led by the USS Enterprise-E in the Delta Quadrant.
The stranded Borg forces that survived slowly began rebuilding their forces in this system. However, soon after retrieving large amounts of dilithium and metal, Species 8472 attacked, destroying what was left of the Federation presence in the Suah'Dron system. The Borg Queen's diamond and a few other Borg ships were able to escape.
Some time later, after the Borg had built up a much larger fleet, they again attempted to capture this system. The Borg Queen decided that the only way to stop Species 8472 was to ally with the Federation, and in order to do that, she needed the assistance of Captain Jean-Luc Picard- and to do that, a transwarp portal would need to be rebuilt in this system. The Borg were successfully able to clear the area of Species 8472 ships, build another transwarp portal, contact Picard, and bring him and his small fleet back home. (TNG video game: Armada II)