- "I am the last of those your kind rose up against and ruthlessly destroyed."
- — The Prisoner of Charum Hakkor to the Ur-Didact
The Forerunner-Precursor War was a conflict in which the Forerunners rose up and destroyed their creators, the race of beings known as the Precursors. The entire Precursor species was believed to be eradicated from the galaxy, leaving only one known Precursor alive. This conflict took place so long before the time of the Didact and Bornstellar Makes Eternal Lasting that their generation had no knowledge of it.
Occuring roughly 10,000,000 years before the Halo Event, the Forerunners were refused the Mantle by their creators, the Precursors. The Forerunners retaliated, driving the Precursors out and killing almost all of them. It is also unknown how the Forerunners managed to defeat the Precursors, even though the Precursors were a Tier 0 civilization and the Forerunners were only Tier 1. However, there are hints that the Precursors allowed themselves to be destroyed, that the Precursors were naive and could not concieve of or defend against retaliation of their own creations. It was also hinted that this beytrayal perverted the Precursors, driving them to only create things to suffer, so that they may never retaliate against their masters again.
Of the very few surviving Precursors, different stratagies for survival were utilized. Many took the form of a fine, desiccated powder that would eventually allow their ressurection. Age perverted this powder, only bringing disease in those that consumed it. The surviving, insane precursors cultivated and controlled this disease, creating the Flood to transform the universe in their new, insane image.