Operation Human Factor

Operation Human Factor, known to the Time Lords as the Human Factor Incident, (PROSE: Dalek Combat Training Manual) was a plot by the Daleks, ostensibly to isolate the Human Factor.

Background
The Dalek Emperor, formerly designated Genetic Variant Two-One-Zero, was inspired to seek the human factor through an encounter with Steven Taylor. Intrigued by his behaviour, the Emperor gave the Daleks a prime directive to discover the human factor. (AUDIO: Across the Darkened City)

The Operation
In a transmission recovered and recorded in The Dalek Conquests, the Daleks located the Doctor's space-time track, positioning him in London, England on the planet Earth in the 20th century time zone, 20 July 1966. Immediately, after the Daleks commenced what they termed Operation Human Factor. (AUDIO: The Dalek Conquests)

The Daleks recruited the Second Doctor, against his will, to isolate and identify the human factor, using Jamie McCrimmon as a test subject. The Daleks claimed that they wished to distill the most important qualities from the factor and use it to make themselves more deadly. The Daleks, in fact, planned all along to use the Doctor's work to identify the Dalek factor. (TV: The Evil of the Daleks)

Once the human factor was identified, it was experimentally transferred to test Daleks, creating three humanised Daleks. The Doctor gave them the names Alpha, Beta, and Omega. He later sabotaged a Dalek machine so that it instilled the human factor into any Dalek that passed through it, converting them into humanised Daleks as well. (TV: The Evil of the Daleks)

The Time Lords believed that the civil war resulted in a temporary absence of Daleks from Skaro. (PROSE: Dalek Combat Training Manual) The human factor was later used to create a whole colony of Daleks on the planet Kyrol. (COMIC: Children of the Revolution)

Aftermath
During the Last Great Time War, the Time Lords made a tactical analysis on Operation Human Factor. With the Doctor having granted them access to the details of his experimental results via the telepathic circuits of his TARDIS, they conducted tests to determine the possibility of distilling a similar "Gallifreyan Factor" whilst research was under way to determine whether any of Humanised Daleks survived, with operatives following up on reports of their potential presence on Kyrol. (PROSE: Dalek Combat Training Manual)

Behind the scenes
The Discontinuity Guide claimed that the Human Factor Incident and the resulting Civil War on Skaro occured somehwere between the 19th century and the mid-22nd century, resulting in the departure of the Daleks from Skaro and leaving the Thals in peace, and that one of the ships that survived the destruction on Skaro crashed on Vulcan in the 21st or early 22nd century, preceding the 22nd century Dalek invasion. Eventually, at some point between the years 3500 and 4000, the Daleks returned to Skaro. It is further noted that, since the Fourth Doctor inadvertently changed Dalek history so that Davros survived, this event would have occurred vastly differently if it happened at all in the new timeline.