The origins of the conflict are unclear but can be traced back to the year 1990 and to some extent even further to 1900. In both of these years the Forever intervened covertly in human evolution by granting them improvements to science, technology and medicine. These advances proved too sudden for humanity to handle and tensions likely arose between the nation states that possessed advanced weaponry. (Unnatural Selection)
The war itself began in some capacity around 2012. It is thought that just one powerful man instigated the conflict. (Waracle). It was likely not total war as it began so early, though more likely some sort of cold war or set of smaller conflicts that escalated as the century went on.
By 2084 the world was on the verge of collapse and the human race facing extinction from both the war and ecological damage to the Earth. Scientists attempted to alter history using the Time Telepathy Project however they were unable to affect any significant changes and so the war reached its cataclysmic end, destroying almost all of mankind. (Prologue, 2084, E=mc 2)
By the end of 2085 any survivors had perished in the radioactive wasteland of Earth. Gamma rays and other destructive forces wiped virtually all evidence of humanity's presence from the Earth, the sixth extinction. (The Sixth Extinction) The only people left alive were Marian colonists. (My House on Mars)