The Gamma Quadrant is the designation for one-quarter of the galaxy, adjacent to the Alpha Quadrant and the Delta Quadrant. Largely unexplored, the Gamma Quadrant was long thought to be inaccessible due to its distance from Federation space. But the discovery of the Bajoran Wormhole in 2369 made the Quadrant accessible to Federation explorers.
Early exploratory missions led to First Contact with species such as the Tosk, the Wadi and the Dosi. But soon Federation exploration attracted the attention of the Dominion, the major power controlling the sectors surrounding the local Wormhole entrance. The Dominion viewed the Federation's expansion into the Gamma Quadrant as an act of aggression, leading to the Dominion War that raged through the Alpha and Beta Quadrants from 2375 to 2377.
Following the end of the War, the Dominion retreated to the Gamma Quadrant. Under the influence of the Founder known as Odo, the Dominion ceased any expansionist behavior, and strictly adhered to its borders, requiring all of its neighbors to do the same. Federation vessels have been warned to stay out of Dominion space. Exploration into the Gamma Quadrant has not been encouraged, nor is it expressly forbidden.
Starfleet is slowly and carefully beginning its exploration of the Gamma Quadrant, first by setting up a deep space station at New Bajor, under Bajoran administration. Opaka Outpost has been deployed in orbit of New Bajor, and serves as Starfleet's base of operations, and hosts the Federation Diplomatic Corps delegation for the quadrant.
Recent observation shows the Dominion beginning to withdraw its presence from occupied worlds - either the Founders have begun decommissioning the Jem'Hadar army, or concerns at the far end of Dominion territory requires their deployment elsewhere. Abandoned worlds have been left to fend for themselves after centuries of Dominion occupation. This has led to disastrous resuts in several cases, as Dominion tactics usually involve rendering worlds completely dependent on the Dominion for one resource or another.
In other cases, local warlords have begun to emerge from the power vacuum, and are vying for control of neighboring systems.
The Stakoron Incident
The Stakoron are a peaceful people. After wo cenuries of Dominion occupation, Stakoron II was abandoned by the Dominion. Stakoron technology had been entirely dependent on the Dominion's supply of sarvinium, which was required to operate the power grid. Federation assistance was required to secure a new supply, and conversion of the Stakoron power grid to standard deuterium power sources is under way.
The Selamat are a telepathic species native to the Gamma Quadrant. Previously known as enforcers for the Dominion, the withdrawal left them without guidance. The Consortium insurgency of 2389 used Selamat telepaths to gain control of Starfleet resources in the Gamma Quadrant, and to mentally control several officers.
List of Gamma Quadrant Species (Memory Alpha)