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“When the Ur-Didact finally exhausted the Humans after a millenia, his sentence was severe. We had no way of knowing that the Forerunners were not your only enemy. Humanity hadn't been expanding; they were running.”

The Human-Flood war was a war fought between ancient humans and the nascent Flood. It took place concurrently with the Human-Forerunner war, and was one of its primary causes.[1] The war destroyed hundreds of worlds, several human-populated systems and cost more than a third of humanity's population. It also forced humanity into war with the Forerunners and contributed to their defeat and de-evolution.

First Flood contact[]

Human ship firing (1)

A human ship fires a bow plasma cannon.

During their colonization of other planets, humans discovered automated cargo ships of unknown origin, which had supposedly arrived from one of the Magellanic Clouds and crashed on planets near the edge of the galaxy. The humans found no crew, but they did find millions of small transparent cylinders filled with an unknown powder. Early tests showed the powder to be harmless and useless, being composed of lifeless short-chain organic molecules. Humans began to test it out on smaller domesticated animals, one of which being the Pheru. The powder tests on the Pheru proved to be initially harmless, and indeed appeared to encourage desirable traits to appear in their appearance and behavior. However, the powder was in fact composed of Flood genetic material, and over time it began merging with and altering the genome of the Pheru in order to generate its own Flood Super Cells. Over time, the infected Pheru began to infect others and even began showing some symptoms of the Flood mutation, such as fleshy tentacle-like rods. Close contact with the Pheru spread the infection to humanity. Some San'Shyuum were also infected as the Pheru were also kept as pets on the San'Shyuum worlds. Eventually the Flood began to spread, and the Feral Phase was initiated.


Human ships and fighter

A small fleet prepares to glass/cleanse a Forerunner planet.

By the time the human officials discovered what the powder had done, it was too late. Entire planets were infected, and the Flood began to ravage worlds and systems. Humans were forced to retreat into Forerunner controlled space, destroying worlds from other species to attempt to halt the spread of the Flood. As quarantine measures failed, human leaders decided to take a third of the population and genetically alter them by inserting genes designed to fight Flood biomass. They then took this third of the population and "fed" them to the Flood. The new genes aggressively killed off Flood bio-matter and destroyed the Flood until the few that survived were forced to into hiding. They would not reappear for another 9,000 years.[1]



Several human ships used during the Forerunner-Flood war, about to be destroyed by Mantle's Approach.

The Human-Flood war ravaged humanity and forced them into a losing war with the highly advanced Forerunners. Unaware of the Flood and the threat it posed, the Forerunners declared war on humanity in order to contain what they saw as an overly aggressive species. With the Flood ravaging human worlds on one front and the Forerunners pressing on another, the Human Empire collapsed. After the Forerunners conquered Charum Hakkor, they scattered the remnants of the race across the galaxy, devolving them to a Tier 7 species. This allowed Flood-controlled Human vessels that had managed to leave the galaxy at the climax of the Human-Flood war a means to sneak past Forerunner defenses unnoticed and would eventually spark the conflict known as the Forerunner-Flood war.



  1. 1.0 1.1 Halo: Cryptum - page 185