Before the official senate was created that still rules in the present day, the Foregunners provided the most stable government in the entire Galaxy. Of the planets they "protected and peacefully observed without interfering", Saurian Ceti IV was one of them. After the SharpYars ancestors attempted to dominate and massacre the other intelligent life on the planet, the Foregunners intervened. After the shockingly defensive SharpYar fought the Foregunners out of Saurian Ceti IV, the Foregunners grew desperate to save the planet. They created three super weapons and placed them in orbit over the planet, which completely destroyed intelligent life. After evacuating the other factions cities, they activated the super weapons and the SharpYar was all but destroyed.
However, a sole vessel of SharpYar managed to flee the planet, and clung to life while intelligent life was being reintroduced. Eventually, the vessel landed on the planet again, and SharpYars way of life was slowly rebuilt.
The Foregunners were experimenting with hyper-lethal bio-weapons, when a "Flood-Troll" virus accidentally broke loose, and quickly took control of the science center that the virus was being developed on. Entire bodies were consumed by the parasite, and turned against the others, furthering the problem. Space Station turned into solar system, and eventually solar system turned into a local cluster of solar systems. The Foregunners were forced to eliminate life in their quadrant of the galaxy, and repopulate it years later, after the Flood was starved of food.