War of Beginnings

The Sangheili-San 'Shyuum War was a interstellar war between the Sangheili and the San 'Shyuum, over religious differences. At the conclusion of the war, the Writ of Union was penned, and the Covenant formed.

After leaving their homeworld, the San 'Shyuum encountered the Sangheili, who also had experience with Forerunner technology. The San 'Shyuum believed that incorporating Forerunner technology was allowed by their religion. To the Sangheili, such a thing would have been unthinkable.

During the combat, the Sangheili had an early advantage, with each warrior comparable in skill to several San 'Shyuum in battle. However, the San 'Shyuum's technological superiority, and possession of the Forerunner Dreadnought, meant that they had the advantage in space, using the Dreadnought to great effect in devastating hit-and-run strikes against the Sangheilian Fleets. Eventually, the Sangheili were forced to amend their position of the treatment of Forerunner technologies and began incorporating elements into their designs.

Eventually, in order to ensure the survival of both races, the two races merged to form the early Covenant with the San 'Shyuum as the head religious leaders and the Sangheili as the physical backbone.