The Longest War
A reset event is a cataclysmic event that happens every so often in the galaxy. These events create a powerful burst of radiation that wipes out all but the most basic life in the galaxy – ‘resetting’ it to primordial stages.
It is theorised that reset events have a period in the region of hundreds to thousands of millions of years, but this has not been confirmed. Often, reset events take the form of large scale supernovae or quasars pointing in the direction of the Milky Way. There is evidence of them scattered all over the galaxy – any given planet that supports life has dozens of unexplained mass-extinction events that were likely caused by resets.
Certain individuals use resets as evidence for intelligent design of the universe, arguing that they always end up happening just as a civilization reaches a certain level of technology.
Resets were discovered in the Milky Way by the Criteks, the first sentient race that we have evidence of. Realising that they would be unable to prevent their own demise, they chose to begin construction of a reset-blocking structure around a star that they expected to cause one in the far future. After that point, dozens of races contributed to the construction before their demise, with humanity nearly completing it. Finally, the Gaijin finished the structure with approximately 100 million years to spare.