1986 Cyberman invasion of Earth

The Cyberman invasion of Earth was an attempted invasion of Earth by the Mondasian Cybermen in December 1986. (TV: The Tenth Planet)

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)

Aftermath
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)