Great Schism (Earth-2042)

"This is the third vector of chaos."

- Zo Resken, former Prophet of Clarity

The Great Schism, also known as the Separatist Schism, the Covenant Schism, or the Great Betrayal among the Sangheili, was a major civil war between the forces loyal to the Covenant and the Confederacy of Independent Systems against the Covenant separatists, which split apart on fall 20 BBY. During the Schism, three major factions fought for victory: the Sangheili Fleet of Retribution allied with the Galactic Republic; the military remnants of the Confederacy of Independent Systems led by the San'Shyuum and the Jiralhanae; and the Flood, which took over the Confederacy's holy capital city of High Charity in an effort to assimilate the other warring factions. The Schism marked both the end of the Covenant and the partition of its client species for a thousand years, as well as the crush of the military might of the Separatists, with only the Separatist Council remaining. For the Republic, it served as a major turning point that led to the end of the war after their disastrous defeat on Reach, and Supreme Chancellor Sheev Palpatine's final step into the closure of the Galactic Republic and beginning of the Galactic Empire.

Source

 * https://www.halopedia.org/Great_Schism