Great Catastrophe (The Exterminators)

The Great Catastrophe was a devastating event that engulfed the galaxy around the late 42nd century, destroying virtually all of the civilised planets and plunging the galaxy into a dark age.

In 4162 the Daleks had invaded the Milky Way galaxy. Within 10-30 years, after a long Dalek War, they had conquered almost everything and established a full Dalek Empire. Susan Mendes and Kalendorf, working against the Daleks, accessed the Dalek Empire's command net through the Dalek Emperor and activated their self-destruct sequence. Whole star systems were destroyed and countless lives were lost. In time, the event became legends that were passed throughout the planets of the galaxy. These legends spoke of a figure known as the "Dark One" or the "Bringer of Death" who was responsible for the Great Catastrophe. (BFDE: Dalek War: Chapter Four)

The Galaxy took 2500 years to recover to the point of resuming interstellar travel.