Cyber Legion

The Cyber Legions were a Cyber-Empire established by a race of Cybermen speculated by one source to be the result of cross-pollination between the Cybermen of N-Space and the Cybusmen of Cybus Industries. By the 52nd century, at least twelve individual Cyber Legions existed.

The Cyber Legions fought against humanity, along with numerous other species, in the Cyber Wars of the 250th Millennium, and were almost completely annihilated when the Tiberian Spiral galaxy was destroyed. However, remnants of the Cyber Legions survived.

Origins
The Cybermen of the Cyber Legions were speculated by one source to be the result of cross-pollination between two Cyber-races: the Cybermen of Mondas and their descendants, (PROSE: The Whoniverse) who had previously fought numerous Cyber-Wars against humanity, (TV: Revenge of the Cybermen et al.) and the Cybermen of Cybus Industries, (PROSE: The Whoniverse) the latter of whom, having failed to conquer their universe's Earth, (TV: Rise of the Cybermen, The Age of Steel) had crossed into N-Space and attempted to conquer its Earth instead, (TV: Army of Ghosts, Doomsday) only to be reduced to scattered remnants across N-Space thanks to the Tenth Doctor, (TV: Cyberwoman, PROSE: Made of Steel, COMIC: The Power of the Cybermen) who sent the vast majority of their forces into the Void, where they ultimately perished. (TV: Doomsday, The Next Doctor) One Cybus unit did find itself in another parallel universe, only to be banished to the Void by the Eleventh Doctor. (COMIC: The Girl Who Loved Doctor Who)

In an instance of parallel evolution, Cybermen identical to those of the Cyber Legions evolved from Neomorphs and CyberMondasians aboard a Mondasian colony ship, and in turn evolved into a "weapons grade version" associated with the Cyberiad. (TV: The Doctor Falls, PROSE: Alit in Underland)

Warfare with humanity
The Cyber Legions eventually fought humanity, as well as numerous other species, in the Cyber Wars of the 250th Millennium, which spanned many decades, if not centuries. During the Cyber Wars, the Cybermen of the Cyber Legions initially resembled the Cybus Cybermen, albeit with a blank circle imprinted on their chest plates instead of the Cybus Industries logo. (TV: A Good Man Goes to War) Some Cybermen that still retained the Cybus Industries logo were also seen. (TV: Nightmare in Silver) Indeed, these Cybermen and their Cyber-ships were known to have joined the Alliance which was embroiled in the Total Collapse Event Incident. (TV: The Pandorica Opens)

However, as the Cyber Wars progressed, the Cybermen upgraded themselves, developing sleeker Cyber-bodies with blue power cells instead of chest plates or chest units, (PROSE: Ghost in the Machine) and developed the ability to upgrade themselves by developing immunities to weaknesses that could be exploited by their opponents; this led to the Cybermen becoming near-invincible. (TV: Nightmare in Silver)

During the 52nd century, shortly before the Battle of Demons Run, the Twelfth Cyber Legion, which monitored the quadrant that Demons Run was located in, was destroyed by the Eleventh Doctor and Rory Williams, in a bid to force the Legion's Cyber-Leader to reveal to them the location of Demons Run. (TV: A Good Man Goes to War) Despite this huge loss, the Cyber Legions continued to be a powerful force in the universe.

In particular, the Ninth Cyber Legion fought across many planets, including Hȳf, Agrippina in a joint invasion with the Eleventh Cyber Legion, Delastrio, Xexos, Aaster, Batraxi, Niami Majora Quintus, Tagarn, Quell, Barranos IV, Cadogan, Praxes, Houndstooth, the sky galleon Drowning Vale, Erodas, and the space station New Cadmus. Although they primarily fought humanity, the Ninth Cyber Legion also faced other species during these conquests, including the Racnoss population of Hȳf, and Judoon, Slitheen and Daleks elsewhere. (PROSE: Ghost in the Machine)

Ultimately, however, the Cyber Legions were annihilated near-entirely, when the Tiberian Spiral galaxy, which the Cyber Legions had used as their "hibernation galaxy", was destroyed, as well as the billions of people living within. (TV: Nightmare in Silver, PROSE: The Mondas Touch)

Survivors
The suits of Cybermen from the Cyber Legions, including two that retained their Cybus logos, were recovered after the Cyber-Wars and became part of Webley's collection at Hedgewick's World of Wonders. (TV: Nightmare in Silver)

Alternate timeline
In an alternate timeline where Rassilon granted a colony of Cybermen at the end of the universe the means to conquer all of history, during the 24th century, the Tenth Doctor noted that if the Cybus Cybermen - who at that point in the timeline had a Cyber-Empire that had brought the Sontarans to near-extinction - successfully conquered Sontar, they would reprogram the Sontaran cloning factories to produce an infinite supply of Mondasians for cyber-conversion; the Doctor described this possibility to Gabby Gonzalez and Cindy Wu as culminating in "an infinite legion of Cybermen, stretching into forever".

Despite the Doctor, Gabby, Cindy, and the Last Great Sontaran War Fleet's efforts, the Cybermen succeeded in conquering Sontar; however, this victory, along with the entire timeline, was ultimately erased from existence when, on Gallifrey at the end of the universe, the Twelfth Doctor and a betrayed Rassilon used the regeneration energy that the Cybermen of the Gallifreyan Cyber Fleet had harvested from the Time Lords and intended to use to forge the Age of the Cyberiad to revert the Cybermen's conquests across time and space by sending the regeneration energy backwards through the Eye of Harmony and the Cyberiad, the latter of which extended across all of history in this timeline. (COMIC: Supremacy of the Cybermen)