
The Flood first entered the galaxy from the Large Magellanic Cloud at the edge of the Milky Way roughly 110,000 years ago, contained in cylinders in unmanned vessels where they were kept as a powder. They sent several ships containing this powder to Forerunner controlled planets. The Precursors saw a chance for revenge and so they created the Flood to destroy the Forerunners as a final act of vengeance against them.

Over time this dust became so corrupted that it could only cause horrific diseases. A few Precursors were spared by the Forerunners, while others became a dust which could regenerate into their past forms.

As the Forerunner-Precursor war drew to a close, the few remaining Precursors that were pushed out beyond the edges of the galaxy to Path Kethona sought vengeance against the Forerunners.
