Cyber Wars of the 250th Millennium

The Cyber Wars of the 250th Millennium (PROSE: The Secret Lives of Monsters) were a series of Cyber-Wars fought primarily between the Cyber Legions and humanity. During the Cyber Wars, the Cybermen devastated the Tiberian Spiral galaxy (PROSE: Ghost in the Machine, A Girl Called Doubt) and used it as their "hibernation galaxy". (PROSE: The Mondas Touch) Although humanity won the Wars through the Tiberian Spiral galaxy's total destruction, at the cost of "a million million lives", remnants of the Cyber Legions survived. (PROSE: The Mondas Touch, TV: Nightmare in Silver)

Origin
The Cyber Wars of the 250th Millennium began when the Cyber Legions formed, speculated by one source to be the result of cross-pollination between the Cybermen of two separate universes. (PROSE: The Whoniverse) The first were the Cybermen of N-Space itself, who had fought humanity on countless prior occasions, (TV: The Tenth Planet et al.) including numerous previous Cyber-Wars. (TV: Revenge of the Cybermen, Earthshock et al.) The second were the Cybermen of Cybus Industries, (TV: Rise of the Cybermen, The Age of Steel) who, after failing to conquer their universe's Earth, and then the Earth of N-Space, (TV: Army of Ghosts, Doomsday) were scattered across N-Space, (TV: Cyberwoman, PROSE: Made of Steel, COMIC: The Power of the Cybermen) the Void, (TV: Doomsday, The Next Doctor) and at least one other parallel universe. (COMIC: The Girl Who Loved Doctor Who)

At least twelve Cyber Legions were active during the Cyber Wars, (TV: A Good Man Goes to War) although the Cybus Cybermen also appeared to fight in the Wars as a separate faction to the Cyber Legions, as evidenced by Webley possessing two empty Cybus Cyberman bodies as part of his collection based in the abandoned Hedgewick's World of Wonders, a thousand years after the Cyber Wars ended. (TV: Nightmare in Silver)

Early Cyberman activity
For a significant portion of the Cyber Wars, the Cybermen of the Cyber Legions possessed Cyber-bodies identical to the Cybus Cybermen, albeit with a blank circle imprinted on their chest plates in place of the Cybus Industries logo. (TV: A Good Man Goes to War, PROSE: Ghost in the Machine)

In the 52nd century, the Twelfth Cyber Legion, which monitored a quadrant of space twenty-thousand light-years away from Demons Run, was infiltrated by the Eleventh Doctor and Rory Williams, the latter of whom breached all fifteen levels of the Twelfth Cyber Legion's flagship and confronted the Legion's Cyber-Leader. Demanding to know the location of his wife, Amy Pond, Rory offered the Cybermen a message from the Doctor; when the Cyber-Leader asked what the message was, the rest of the Twelfth Cyber Legion's Cyber-ships exploded. With almost all of its army destroyed, the Cyber-Leader conceded and revealed the location of Amy to the Doctor and Rory, and the duo left to rescue her from Demons Run. (TV: A Good Man Goes to War)

Conquests of the Ninth Cyber Legion
After acquiring a fragment of the Eternity Clock, the Ninth Cyber Legion time travelled to Earth in 2012 and conquered London, where they set up a Cyber-factory and began mass-converting the city's population. However, the Eleventh Doctor and River Song successfully infiltrated the Cyber-factory and shut down its thermionic core, escaping through a time corridor with the Legion's Eternity Clock fragment immediately before the Cyber-factory exploded. The remains of numerous Cybermen remained scattered across London as far as 2106, when the New Dalek Paradigm attempted to invade Earth with their own fragment of the Eternity Clock. Ultimately, following the defeat of the Paradigm's Dalek Emperor by the Doctor and River Song, the Ninth Cyber Legion's invasion of London, as well as all the other conquests achieved by the Daleks, Silurians and Silents with the Eternity Clock's fragments, was erased from history. (GAME: The Eternity Clock)

The Ninth Cyber Legion also invaded numerous other places during the Cyber Wars, and subsequently fought humanity and several other species on many occasions.

Thousands of Cybermen of the Ninth Cyber Legion invaded Hȳf and fought the planet's Racnoss population; the Legion's Cyber-Controller used the battle to test a new model of Cyber wrist blaster and assess the possibility of incorporating it into future Cybermen. During the battle, the Cybermen inflicted greater casualties onto the Racnoss than the Cybermen sustained themselves. After departing Hȳf, the Ninth Cyber Legion allied with the Eleventh Cyber Legion to conquer Agrippina in the Tiberian Spiral, with both Legions fighting at opposite poles of the planet. The battle was a far greater strain on both Cyber Legions than the attack on Hȳf had been for the Ninth Legion; thousands of Agrippina's human population were converted, but thousands of Cybermen were in constant need of repairs. (PROSE: Ghost in the Machine) Although the Cybermen's conquest of Agrippina was ultimately a success, thousands of heavily-damaged Cybermen were left behind, particularly in Agrippina Primus, as the Cyber-Leaders of the Eleventh Cyber Legion considered the energy expenditure necessary to repair these Cybermen to be greater than if the Legions simply converted other worlds to replace the damaged Cybermen. (PROSE: A Girl Called Doubt)