Great Inferno

The Great Inferno, (COMIC: Terrorformer) or Hyperion War, (COMIC: The Fractures, Gangland) was a war between the Alliance of Races and the Hyperions.

Origins
When the Hyperions started subjugating other races and draining their suns of sustenance, Rassilon assembled an alliance of most powerful races in the universe, which included, among others, Time Lords, Hath, Ice Warriors, Judoon, Silurians, Sontarans, Vigil and Zygons.

Hostilities
Thousands of years before the 25th century, to prevent their own worlds from being targeted, the Alliance of Races declared war on the Hyperions and extinguished the fires of Hyperios, the homeworld of the Hyperions. (COMIC: Terrorformer, The Hyperion Empire)

Aftermath
However, a few Hyperions survived by fleeing and hibernating in remote corners of the universe, including on Isen VI (COMIC: Terrorformer) and Neptune. (COMIC: Terrorformer, The Hyperion Empire)

The Alliance of Races continued after the Hyperion war, purging other "threats to universal harmony", including the Cybock Imperium. (COMIC: Gangland) Enough individuals were left in Time Lord incarceration that Rassilon created the Rassilon cubes. (COMIC: The Fractures)