1986 Cyberman invasion of Earth

The Cyberman invasion of Earth was an attempted invasion of Earth by the Mondasian Cybermen. (TV: The Tenth Planet) Following the CyberFaction's invasion, this was the second Cyberman invasion of Earth recorded both in the history computer of the CyberFaction (PROSE: Iceberg) and in the Cyber-Documents of Earth, which were compiled into the CyberHive by the ArcHivist Hegelia. (AUDIO: The Early Cybermen)

Dating
Most accounts agreed that it occurred in December 1986. (TV: The Tenth Planet, PROSE: Iceberg, Mondas Passing, AUDIO: The Reaping) However, others placed it in the 1990s (PROSE: The Power of the Daleks) or the year 2000. (PROSE: Doctor Who and the Tenth Planet, Doctor Who and the Tomb of the Cybermen)

Origin
"Eons" prior to the invasion, Earth and Mondas were twin planets before Mondas drifted away to the edge of space. (TV: The Tenth Planet)

Scout crafts from Mondas were sent to find Earth's location. The first expedition to find Earth crash-landed in the mountains of Austria around 1873, 113 years before their invasion. (TV: The Tenth Planet). However, due to the extensive damage sustained during the landing, they failed to report the location of Earth to Cyber-Control on Mondas, which was 200 light-years away. The Eighth Doctor made sure that all Cyber-Technology from the expedition was destroyed. (AUDIO: The Silver Turk)

The Seventh Doctor and Ace fought Cybermen in Nevada in 1954. These Cybermen were from Mondas, trying to invade. Their attack was delayed until 1986. (COMIC: The Good Soldier)

In 1970, the Cybermen attempted to disarm all of Earth's armies so that they could take over the planet without the death of a single Cyberman. Three Cybermen landed in the English countryside in a rocket and began tunnelling with a Cyber-Mole. With the Mole, they stole the doomsday bomb from Earth's underground secret weapons store and used it to put the entire Earth at ransom. The Second Doctor and John walked down the tunnel left by the Cyber-Mole and killed the Cybermen with ray guns before they could detonate the bomb. (COMIC: Cyber-Mole)

When Earth's most brilliant scientists gathered to witness the test flight of the Dart, Cybermen attempted to kidnap all of them to weaken Earth's military progress. The Second Doctor worked with the United States Air Force to destroy the Cyberman spaceships before the scientists could be taken. (COMIC: Test Flight)

In 1984, two years before the return of Mondas, the Sixth Doctor left a damaged Cyber-Leader from the far future on Mondas, where it was considered faulty by its ancestors and taken to be reprocessed. (AUDIO: The Reaping)

The invasion
Eventually, Mondas would arrive in Earth's solar system in the year 1986. The First Doctor met an advance force of Mondans near Snowcap Base in Antarctica. This force was to prepare for Mondas' return to the Sol system and to drain Earth's energy for the Cybermen. Mondas absorbed too much energy and was destroyed, as were the Cybermen on Earth who depended on Mondas for power. (TV: The Tenth Planet)

The Doctor
Shortly following the destruction of Mondas, the exhausted First Doctor began his regeneration. Though he was initially reluctant to change, he was convinced to do so following an encounter with the dying Twelfth Doctor who, unwilling to regenerate himself, was taken back to his own past by the TARDIS. (TV: The Tenth Planet, Twice Upon a Time) Incidentally, the Twelfth Doctor had also been forced to the brink of regeneration by a conflict with the Mondasian Cybermen. (TV: World Enough and Time/The Doctor Falls) Ultimately, the two Doctors parted ways and regenerated into the Second and Thirteenth Doctors respectively. (TV: The Tenth Planet, Twice Upon a Time)

Ben and Polly
Twenty years after they helped the First Doctor prevent the return of Mondas in the then-future year of 1986 in their personal timelines, Ben Jackson and Polly Wright — who had gone their separate ways in life following a brief relationship after their return to Earth on 20 July 1966 — reunited on New Year's Eve in 1986, which was by then their present. Ben believed that numerous governments may have covered up the return of Mondas and the Cybermen invasion of the Snowcap. (PROSE: Mondas Passing)

Earth
Professor Allison Williams led the scientific team which investigated the Cyberman ship in Antarctica. (PROSE: The Power of the Daleks) The Cyberships leftover from the invasion were examined and exploited by humans, allowing them to make advances in space travel, leading Sarah Jane Smith to describe the return of Mondas as "both the greatest disaster and most astonishing blessing ever to have happened to the human race." (PROSE: The Power of the Daleks)

The Cybermen
As late as 2070, Earth history books recorded that the Cybermen were all wiped out when Mondas was destroyed. However, there were groups of Cybermen that travelled into space prior to Mondas' destruction. The first settled on the planet Telos. These Telosian Cyberman returned to the solar system on 15 October 2070. Seeking the power used to destroy Mondas, the Cybermen infiltrated the human base on the Moon, when they intended to use to wipe out all life on Earth. They were opposed by the Second Doctor who accused the Cybermen of being motivated by revenge, while the Cybermen claimed that they were acting to eliminate dangers to the Cyberman Empire. Ultimately, their invasion attempt was thwarted by the Doctor. (PROSE: Doctor Who and the Cybermen, TV: The Moonbase)