Flood-Borg War

The Flood-Borg War was an ancient conflict shrouded in mystery that has only come to light after intense studies of Forerunner Relics that determine the exact nature of the Forerunner-Flood War that occured thousands of years ago. The War between the Flood and the Borg was kept a secret by the idiotic Forerunner Council so that the population of the Galaxy wouldn't get any ideas and stop paying their 'War Taxes' that the Forerunners forced upon them when their civilisation was at its worst.

The war between the Flood and the Borg spans back to when the Flood were a completely different life form called the Precursors. The Precursors were obsessed with forming a super-race that would consume the entire Galaxy, to create a massive collective that would eliminate pain, suffering and other forms of social malcontent that plagues all forms of sentient life in the Galaxy. The Precursors believed this to be the only answer, and so they initially created the Borg - a race that would stop at nothing to assimilate every other race in the Galaxy. When their plan went wrong, however, and the Flood was born from the mutiliated flesh of the Precursor race, a natural rivalry formed between the Flood and the Borg that soon escalated into all-out war.

The Flood and the Borg did not meet each other for nearly a millenium, but as soon as they did there were hostilities on every front. Borg Cubes amassed above Flood-Controlled worlds and attempted to assimilate them, but the Flood were naturally immune to Borg assimilation and slaughtered the cyborg warriors by the thousands. The fury of pure flesh that the Flood formed into natural weapons proved too much for the Borg, who could not adapt to defend themselves against physical attacks. Their many attempts to outmaneuver the Flood proved fruitless, and they were pushed out of the Milky Way entirely, forced into the primitive recesses of the Trek Galaxy, which would not be colonised by the League for several thousand years.