What is the setting of Dark Force Rising by Timothy Zahn?

Dark Force Rising takes place five years after the Battle of Endor, during which both the Emperor and Darth Vader perish and the last surviving Grand Admiral, Thrawn, takes control of the Empire. Rumors leak out to the New Republic of his existence, but his name is not generally known. Further back, a half-century, the Old Empire's Katana fleet, also known as the "Dark Force," disappeard and a warship crashed on the Noghri planet Honoghr and pollution from it ostensibly poisons the planet.