Stardate 46922.3: A Valerian transport will soon be docking at Deep Space Nine, much to the chagrin of Major Kira, who knows that the Valerians had once been a supplier of chemical weapons to the Cardassians during the Occupation of Bajor. Before the ship enters the sector, however, the Klingon vessel Toh'Kaht, on a bio-survey of the Gamma Quadrant, returns early through the wormhole and promptly explodes before the DS9 crew's eyes. One of the Klingons had been able to beam aboard the station while the Toh'Kaht exploded. Just before he succumbed to phaser blast injuries, he speaks the word, "Victory".
When the Cardassian occupation of Bajor ended in 2369, the mining space station Terok Nor was left abandoned, its systems ripped out. By invitation of the Bajoran provisional government, Starfleet stepped in to oversee the rebuilding and day-to-day operations of the newly christened Deep Space Nine.
The years of Starfleet's nonintervention into Cardassian matters, however, had taken its toll on relations with the Bajorans. Consequently, Starfleet's position was a tenuous one; many Bajorans, suspicious and hostile as a result of decades of Cardassian oppression and brutality, did not greet the Federation's presence with open arms. The Federation's assistance is put to the test as DS9 becomes a center of travel and commerce that stretches into the Gamma Quadrant.