Galactic Cycles

The galaxy goes through cycles of growth and resets one after another.
In the millennia of history passed, there have been countless races that have at one time arisen from their cradles. For many thousands of years, civilization would flourish and life would fill the galaxy. Yet, inevitably, some force would, without fail, bring it to an end.
Then the cycle would begin again.

The most recent cycle of the galaxy started some 70,000 years ago. Within the the start of the latter half of that period, the Kahz rose to prominence. Despite there having been nearly forty thousand years in between the end of the previous cycle and the rise of the Kahz, there is no evidence of any spacefaring activity during that time. It may have been a mere few thousand years, but the time in between the rise of the Kahz and any other species was sufficient for them to dominate much of the Orion arm. This seems to be the standard of local resurgence for galactic cycle, as rarely do two races emerge in the same region of the galaxy at the same time.
It is the destruction of sapience at the end of each cycle that leaves the galaxy so empty, as it awaits new species to achieve the cognitive threshold. As it was with the Kahz, one race will eventually rise to regional dominance. Once a race discovers the Express, exploration and colonization progresses at a much faster rate. Records of the last cycle remain for discovery and the nature of the galaxy is sometimes discerned. Yet it is unclear if any race has ever avoided their fate. Some put effort into exploring the galaxy for clues, while a few have tried to leave the galaxy altogether. The time span between cycles is hard to discern, even with the knowledge left behind from the last one. There seems to be an irregular time span between resets, although there is always more than enough time for sapient races to once again arise.