A neutronic war was a war fought with neutron bombs, just as a nuclear war was a war fought with nuclear weapons. A neutronic war was fought between the Thals and the Humanoid Daleks, which led to the mutation of both races and the creation of the non-humanoid "machine Daleks", and the ravaging of their homeworld, Skaro. (TV: The Daleks, COMIC: Genesis of Evil)
Accounts differ as to the reasons for the war. According to one history recorded a long time afterwards, the war was deliberate. (TV: The Daleks) According to another, the detonations of the neutron bombs were an accident caused by a meteorite strike. (COMIC: Genesis of Evil)
Human historians came to believe that the Neutronic War was a short conflict waged in the immediate aftermath of the Thousand Year War where the Thals, though weakened by the attack on the Thal Dome, attempted to destroy the burgeoning Dalek race who responded by detonating a neutron bomb. (PROSE: Dalek: The Astounding Untold History of the Greatest Enemies of the Universe)