Stardate 49556.2: For betraying Chancellor Gowron by not fighting at his side against the Cardassians ("The Way of the Warrior"), Worf's House was punished with the loss of his lands and the banishment from the Empire. While the exile damaged Worf, it hurt his brother, Kurn, most of all. Kurn shows up at Deep Space Nine seeking his brother so that Worf can perform the Mauk-to'Vor and send his brother across the river of blood into Sto-Vo-Kor and the afterlife.
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.