Genesis timeline

By one account, following the Fourth Doctor's mission to interfere with the creation of the Daleks on their behalf, the Time Lords observed that changes to the timeline had freed thousands of worlds from the tyranny of the Daleks, but not the millions hoped for. Following the Doctor's subsequent actions in the weapons research facility of Deepcity, however, the Time Lords foresaw the rise of a race of robots that would challenge the Daleks and lead to the fall of the Dalek Empire. (PROSE: A Device of Death) By another account, the Celestial Intervention Agency's own documentation, the mission to Skaro had ended up a bootstrap paradox, as the Doctor's actions only ensured the timeline they were already living in had come to pass. (PROSE: The Dalek Problem)

Regardless, numerous observers including the Doctor themself saw the mission as the "first shot" (AUDIO: The Dalek Conquests, The Innocent, The Eternity Cage, PROSE: Engines of War, The Astounding Untold History of the Greatest Enemies of the Universe, COMIC: Hunters of the Burning Stone) of what ultimately became the Last Great Time War, a conflict which had far-reaching consequences across the history of the universe. (PROSE: The Whoniverse, The Astounding Untold History of the Greatest Enemies of the Universe, Dalek Combat Training Manual) Indeed, the Daleks did at some point become aware of the Time Lords' attempt to subvert their development, which they henceforth viewed as the Gallifreyans having launched a pre-emptive strike and act of aggression. (PROSE: The Slyther of Shoreditch, WC: , AUDIO: The Dalek Conquests, The Innocent, The Eternity Cage) The Tenth Doctor later admitted that, for the Daleks, their history was "confusing enough" before the Time War. (PROSE: Prisoner of the Daleks) In a parallel universe in which he chose to destroy the Daleks, the Fourth Doctor was embroiled in the Time War as it started prematurely, regenerating into the Warrior. (AUDIO: Dust Devil)

Behind the scenes

 * The Discontinuity Guide made the claim that, originally, Davros was killed and forgotten, and that the Fourth Doctor's interference with the creation of the Daleks created a new timeline where Davros survived, the Doctor's warnings about the Daleks having made Davros paranoid enough to activate a force field in his chair. As a result, whilst the Daleks originally had a solid, cohesive empire, always with one purpose, Davros' presence reduced them to "a mess of squabbling factions" which were "incapable of the unity needed to develop dimensionally transcendental time travel." Published before the Last Great Time War was established in Doctor Who lore, The Discontinuity Guide went on to claim that "whilst Davros lives the Daleks will remain disorganised, and will never become the threat that the Time Lords so feared."
 * In a deleted scene from the end of Return of the Cybermen, the Time Lord messenger would have appeared in the TARDIS to tell the Fourth Doctor that his failure to succeed in his mission had caused his own history to reoccur in slightly different ways and may lead to a Time War. This was meant to explain the contradictions between Return of the Cybermen and Revenge of the Cybermen, as well as between The Haunting of Villa Diodati and Mary's Story, and Human Nature and Human Nature.