Tenth Dalek Occupation

The Tenth Dalek Occupation was the final major event known to involve the Daleks before the outbreak of the Last Great Time War. (PROSE: A Brief History of Time Lords)

One historical account considered the period among the last events of the Dalek Wars. (PROSE: The Whoniverse)

Prelude
In their record of Dalek activity in linear history, the Time Lords of the Time War placed the Hand of Omega Incident and the subsequent destruction of Skaro during the Imperial-Renegade Dalek Civil War in the "far future", following the 47th century Necros Incident and preceding the Daleks' entry into the Last Great Time War. (PROSE: Dalek Combat Training Manual)

Disappearance of the Daleks
The author of A Brief History of Time Lords recorded that the Daleks vanished from time and space after the Occupation. Galactic folklore held that "they had gone off to fight a bigger war".

Subsequently, the Dalek Emperor launched the Dalek forces into the Time Vortex, beginning the Time War. (PROSE: A Brief History of Time Lords)

Jack Harkness, a 51st century Time Agent, noted that the Daleks were "the greatest threat in the universe" before their sudden disappearance, which the Ninth Doctor confirmed was so they could fight the Time War. Though Jack had believed the Last Great Time War to be just a legend, (TV: The Parting of the Ways) he recognised the design of Dalek flying saucer used in the conflict, (TV: Bad Wolf) having seen them during the Occupation (PROSE: Doctor Who: The Encyclopedia) originally believing that they had been destroyed. (TV: Bad Wolf)

Human historians following the Siege of Trenzalore knew records which stated that the Daleks disappeared following a "long period of Dalek occupation". (PROSE: Dalek: The Astounding Untold History of the Greatest Enemies of the Universe)

Return of the Daleks
Whilst fighting their relentless enemy, a ship of Daleks were flung through a temporal schism to the 64th century, where they confronted humans who believed the Daleks to be extinct. (PROSE: Lost Patrol)

In 200,100, the Dalek Emperor, having survived the Time War, launched an invasion of Earth with his army of Daleks. Rodrick, an Earth human, was sceptical as to the return of the Daleks, recalling that they had all disappeared thousands of years prior. (TV: The Parting of the Ways) A separate Dalek survivor intended to leave 21st century Earth to rebuild in 500,000,000, where it was aware that no-one would know of the Daleks, only to be destroyed before it could do so. (PROSE: I Am a Dalek)

The first Daleks of the New Dalek Paradigm, who were created in 1941 by survivors of the New Dalek Empire, were intended to return to their "own time", which the Eleventh Doctor knew to be in "the future", where they were to "begin again". Ultimately, he failed to prevent the Daleks from escaping via a time corridor. (TV: Victory of the Daleks) The Daleks set their sights on Skaro, their home planet which had been left abandoned and in ruins following the Time War. Though an initial attempt at recovering the planet was averted by the Doctor, (GAME: City of the Daleks, TV: Asylum of the Daleks) the Daleks eventually succeeded in rebuilding and repopulating Skaro. (TV: The Magician's Apprentice/The Witch's Familiar)

Behind the scenes
The Tenth Dalek Occupation is mentioned in a few sources, but A Brief History of Time Lords is the first in-universe source, and therefore the first valid source, to both name and detail anything about the event.

Jack's line in The Parting of the Ways - "One minute [the Daleks are] the greatest threat in the universe, the next minute they vanished out of time and space" - could originally just have been a generic assessment about the overall danger posed by the Daleks. However, this line largely serves as the foundation on which the fictional history of the Occupation is built. A Brief History of Time Lords, plus other reference materials, later attributed this period to the end of the Occupation, thus making The Parting of the Ways the first story to allude to the Occupation, if retroactively.

The Time Traveller's Almanac states that the Tenth Dalek Occupation was the last time that humans had seen the Daleks before the Emperor returned from the Time War to invade Earth in 200,100.

In The Dalek Handbook, the Tenth Dalek Occupation is said to have occurred some time after the trial of on Skaro, although the relevant dates are unknown. Prior to the Dalek-Movellan War, the Daleks had maintained a reputation as the greatest threat to the universe, yet that conflict had kicked off a period of stagnation and then infighting. The Tenth Dalek Occupation, therefore, was the Daleks' return to power after the conclusion of the Imperial-Renegade Dalek Civil War. Collating details that can be gleamed from other stories, primarily The Parting of the Ways, as above, its brief account of the Occupation reads: "... the Emperor of the Daleks led his renewed race to become truly the greatest threat to the universe. The Daleks had grown in power and technological ability and now waged war on the cosmos, and especially on the human race, in a period of aggression that culminated in the Tenth Dalek Occupation. After which... nothing. The Daleks vanished from time and space."