One timeline of 2040, in which numerous incarnations of the Doctor gradually prevented the Perseus Corporation from integrating humanity into the Ethereal, (PROSE: The Ethereal, et al.) was created by the Seventh Doctor meddling with history. (PROSE: The Nuclear Option) This timeline notably overlapped with a universe where a version of the Doctor became stranded on Earth in 2039. (PROSE: Sustainable Energy)
This timeline was a divergence from Chris Cwej and Roz Forrester's native timeline. In the original 2040 timeline, a CIA-backed terrorist cell caused a nuclear explosion at Toronto's Pickering power station as a decisive step in America's takeover of Canada. The Seventh Doctor decided to change history by averting these events, using Cwej and Forrester to influence the terrorists and stop them while also publicly exposing the CIA plot. The new timeline took a period to stabilise, chaotically overlapping with the other reality, but it soon stabilised. (PROSE: The Nuclear Option)