Rutan-Sontaran War

The Rutan-Sontaran War between the Rutan Host and the Sontaran Warburg lasted for millions of years across Mutter's Spiral.

Origins of the War
The Sontarans, at that stage not yet a species of clones, but already, according to the Doctor, a "fierce, martial race", began to sweep over Mutter's Spiral. Only the Rutans stopped them. Reacting to this, the Sontarans stopped reproducing naturally and began to turn themselves into a clone species. (DWM: Pureblood)


 * The Doctor described this event as "ten centuries" before the 25th century, meaning that the conflict would have begun in the 15th century. This contradicts evidence given elsewhere, such as a Sontaran speaking of war with the Rutans in the 12th century as well as both Rutans and Sontrans involving themselves in the Millennium War of 150 million years before.

Events in the War
During the 12th century (DW: The Time Warrior) and the 1900s (DW: Horror of Fang Rock), Earth assumed strategic importance by the Sontarans and Rutans respectively, who tried to make the planet into a military base for their respective species.

In the 1980s, the Sontaran Warburg investigated the possibility of using TARDIS-like time ships in order to win the war. (DW: The Two Doctors)

After solar flares devastated Earth, a Sontaran scout landed in hopes of exploiting the planet's strategic importance. (DW: The Sontaran Experiment)

Involvement of Gallifrey
Though the Sontaran Linx, in the 12th century, merely considered the invasion of Gallifrey as a speculative possibility (DW: The Time Warrior), the Sontarans, in concert with the Vardans did invade, until beaten back by then-Lord President the Doctor. (DW: The Invasion of Time)

During another period of Time Lord history, the Warburg, led by General Sontar himself, the Warburg's supreme commander, and the Rutan Host convened on Gallifrey to meet face to face without violence. (PDA: The Infinity Doctors).


 * When this two encounters with the Time Lords occurred in unknown, due to the difficulty in dating the Time Lord stories.