Cyber-Wars

The Cyber-Wars was a galactic conflict in which a concerted effort by a united force set out to wipe out the Cybermen in 2526. A group of time-travelling Cybermen from the end of the conflict tried to prevent this by destroying the Earth with a Cyber-Bomb and then by crashing a human freighter into the Earth, but both these attempts were stopped by the Fifth Doctor. (DW: Earthshock)

It was during this time that the glittergun was developed as a weapon against them. It would fire gold dust at Cybermen, gold being a major weakness of theirs. The Wars resulted in near-complete destruction of the Cyber race, with remnant groups of Cybermen fleeing across the galaxy.

Many Planets were destroyed in the War.

Post-War

 * The majority of surviving Cybermen put themselves in suspended animation on the planet Telos, waiting for future opportunities. (DW: The Tomb of the Cybermen)
 * One remnant tried to destroy Voga, the planet that supplied the majority of gold for the Cyber-Wars. (DW: Revenge of the Cybermen)
 * One derelict Star Destroyer ended up in the Garazone System, and was reactivated some fifty years later when the Earth Empire tried to collect Cyber-Technology for use in the Orion War. (BFA: Sword of Orion)
 * One cruiser crashed in the oceans of Earth, and was salvaged by humans, again for use in the Orion War (BFA: Cyberman: Scorpius)