Millennium Wars

You may be looking for the Millennium War.

Having temporary control of the Event Synthesizer and therefore over reality itself, the demon Melanicus instigated, for no other reason than to do it, the Millennium Wars, encompassing a thousand different worlds and a thousand different time periods. (DWM: The Tides of Time)

The worlds ruined by the Wars included a future Earth. (DWM: The Tides of Time)

The Fourth Doctor was briefly caught in one of these conflicts, not understanding its signifcance. (DWM: The Deal)

With the defeat of Melanicus by the Fifth Doctor and Sir Justin and the restoration of the Event Synthesizer to its rightful operator, the Millennium Wars may have vanished from history.