2180s Dalek invasion of Earth

In the late 2180s, the Dalek Time Controller, a Dalek from the future, organised a second invasion of the planet Earth, following the invasion which was thwarted two decades earlier.

The Daleks were helped by the Time Lord known as, who brought on Earth a plague that killed and affected a number of people. The Monk was promised to be allowed to plunder the art treasures of the planet in return for his technical expertise. The Monk made three major contributions to the invasion; firstly, he repaired the Dalek Time Controller when it was blasted back through the Time Vortex, and was in a state of decay beyond the Daleks ability to repair. Secondly, the Monk was personally responsible for unleashing a virus into Earth's atmosphere which was beyond the humans' ability to stop it, killing millions and weakening the planet ready for the upcoming invasion. Lastly, the Monk provided the resistance with the technical ability to hack into Dalek transmissions during a final attempt to end the invasion, but he betrayed them to the Daleks.

The master plan was to pilot the Earth with a time warp engine, which would have become a plague planet teeming with the Amethyst viruses, through time and space, infecting entire planets. The invasion was stopped by the Eighth Doctor, thanks to the sacrifice of Lucie Miller and Alex Campbell. (AUDIO: Lucie Miller / To the Death)

Legacy
In the aftermath of the invasions, many humans remained paranoid about another alien incursion and took to carrying weapons on their person. (AUDIO: All Hands on Deck)

Following the second invasion, Susan made her home in a block of flats which had once been Coal Hill School. Despite the Doctor's efforts to distract her, Susan found that she had been sent Hypercube messages from the Time Lords, who were engaged in a time war against the Daleks. Citing her participation in the resistance against the two Dalek invasions on Earth as well as reasoning that the Daleks would ultimately return should the Time Lords fall, Susan decided to accept their request and join the war despite the Doctor's protest, summoning a TARDIS to collect her. (AUDIO: All Hands on Deck) By another account Susan was still on Earth fifty years after the first invasion, encountering the Thirteenth Doctor as she was on her way to a pyre of Dalek technology. The Doctor showed her the remains of a dead Dalek, shich Susan could take out her anger on. (PROSE: Fellow Traveller)

In the post-Time War universe, following the Siege of Trenzalore, "some" historians believed in the story of the Daleks' second 22nd century invasion. In any case, Earth eventually flourished in the aftermath, with humanity finally heading out to the stars to establish its own Empire. (PROSE: Dalek: The Astounding Untold History of the Greatest Enemies of the Universe)

Behind the scenes

 * The third edition of AHistory speculates that the events of Legacy of the Daleks became an alternate timeline when and the Dalek Time Controller rewrote history to enable a second Dalek invasion in the 2180s, as seen in Lucie Miller and To the Death, but admits that this doesn't explain how Susan can have a child with David, or how  ended up on Tersurus in.