In Star Trek: Deep Space Nine, The Bajoran Wormhole is the only known stable wormhole, providing a quick path between the Alpha and Gamma Quadrant.. It was discovered by Commander Sisko in May of 2369 who promptly moved Deep Space Nine to its Alpha Quadrant entrance thus claiming that space for Bajor and providing the potential to revive the shattered Bajoran economy.
The wormhole was regarded as Celestial Temple by the Bajorans who worshiped the wormhole aliens known as The Prophets. Because he discovered the wormhole, Sisko was heralded as the Emissary.
Controlling the Alpha Quadrant entrance to the wormhole benefited the Bajorans as it was a major trade route from then on, but within a year it began clear that it posed a threat to the Alpha Quadrant. A militant race called the Jem'Hadar, themselves soldiers for the Dominion, a vast Gamma Quadrant empire controlled by a race known only as The Founders. The Dominion was bent on conquering the entire Alpha Quadrant and before long, war broke out between the Klingons and the Dominion, and shortly afterwards the United Federation of Planets joined in.
In 2373 or 2374 the Federation mined the Wormhole with self-replicating mines to prevent any more Dominion ships from entering the Alpha Quadrant, and shortly afterwards Deep Space Nine was captured by the Dominion with the help of their newest members: the Cardassians. (Call to Arms)
In March of 2374 the Cardassians managed to disable to mines and the Dominion fleet prepared to invade, but Captain Sisko, flying into the wormhole to attack the fleet head-on with a single ship is contacted by the Prophets whom he convinces to stop the Dominion. They then agree to use their power to destroy any war-related traffic through the wormhole, and Sisko is able to retake Deep Space Nine (Sacrifice of Angels).
In 2374 or 2375, Gul Dukat released the Pah-Wraith--an evil Prophet--which entered the wormhole. The wormhole then closed up (Tears of the Prophets).
In late 2375 the wormhole re-opened after Cardassia fell and the Dominion War was finally won by the Federation-Klingon-Romulan alliance and Sisko trapped the Pah-Wraith in it's ancient prison in the Fire Caves. Sisko then joined the Prophets in the wormhole. (What You Leave Behind)