Thousand Year War

The Thousand Year War pitted two indigenous peoples of Skaro, the Kaleds and the Thals against one another. The conflict ravaged the planet, with radiation forcing the remaining combatants to live within domed cities. The war created a third race of sorts in the Mutos, made outcasts due to their disfigurement. Even as the cause of the war was lost to memory, both sides remained committed to victory - and the Kaleds achieved a scientific breakthrough when Davros engineered the Daleks.

Causes
By the latter stages of the war, neither the Kaleds nor the Thals could remember why it had started. (AUDIO: Davros)

By the time that the Fourth Doctor visited Skaro on a mission to prevent the creation of the Daleks, the Thals and Kaleds lived in two domed cities overlooking a polluted wasteland. The Scientific Elite, headed by Davros and his assistant Nyder, and a Military Elite hoped to create weapons that would finally bring victory. The use of nuclear, chemical and biological weapons had led to genetic mutations among both Thals and Kaleds, disparagingly referred to as Mutos. The Mutos were driven out by the Thals and the Kaleds to keep their races pure.

By this time, so many of the Kaleds and Thals had died that they resorted to commissioning boys in their teens and twenties as military officers. (TV: Genesis of the Daleks)

Weapons and technology
An anachronistic mixture of technologies on the battlefield showed a society which had devolved rather than evolved, with combatants using energy weapons alongside rifles and machine guns and engaging in trench warfare as in Earth's early 20th century. Their uniforms were frequently mismatched - soldiers could be seen wearing modern combat jackets made of synthetic fibre with other articles of uniform made of leather.

In the long-range, as well as the biological and nuclear weapons already mentioned, both sides used chemical rockets. Towards the end of the war, the Thals intended to use a neutronic missile against the Kaleds. (TV: Genesis of the Daleks)

Conclusion
The war did not conclude so much as peter out. Davros gave the Thals information to allow them to breach the Kaled Dome, causing massive casualties amongst Davros' own people.

This provided a rationale for the Kaleds in turn to set the newly created Daleks against the Thals. At last, a Thal rocket destroyed the Kaled Dome. Thals, led by Bettan, and Mutos, led by Sevrin, joined to fight against the Daleks emerging from the ruined Kaled city. (TV: Genesis of the Daleks)

A contradictory account by the Daleks and the Thals from over five hundred years after the war ended described the war as just a quick neutronic war, and not lasting for centuries. According to Alydon, Skaro, which Alydon described as "a great world, full of ideas and art and invention", was destroyed in one day. (TV: "The Expedition") One Dalek claimed that after the neutronic war, the Daleks' "forefathers" retired into the Dalek City, and protected themselves from the fallout inside their machines. (TV: "The Survivors")

Behind the scenes
Rhyfel Mil Flwyddyn Tausendjähriger Krieg
 * According to the non-narrative reference book Doctor Who: The Dalek Handbook, the war lasted from 450 AD to 1450 AD.