Cyber-Wars

The Cyber-Wars was a galactic conflict in which an alliance made a concerted effort to wipe out the Cybermen in 2526. It lasted for 1,000 years. A force of time-travelling Cybermen from the end of the conflict attempted to prevent this. They tried to destroy the Earth, first with a Cyber-bomb and then by crashing a human freighter into the Earth. Both of these attempts were stopped by the Fifth Doctor. (TV: Earthshock)

It was during this conflict that the glittergun was developed. Gold was a major weakness of the Cybermen. The gun could fire gold dust at them.

The wars resulted in near-complete destruction of the Cyber race. Remnant groups of Cybermen fled across the galaxy. (TV: Revenge of the Cybermen)

It ended up being settled when the entire galaxy was destroyed Nightmare in Silver (TV story). The Cyberwars ended, but some Cybermen had survived, and continued to threaten the universe.