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.

Trivia

 * interestingly the Sangheili-San 'Shyuum War resembles a conflict that occured in a hit japanese show called "Dragon Ball" were the planet Vegeta was home to two races: the Tsufurujin and the Saiyans. The Tsufurujin were a diminutive race, native to planet Vegeta, who lacked physical strength and toughness, but were very intelligent and skilled with technology. By contrast, the Saiyans were human-sized, but very strong and brutal. The Saiyans did not originate from planet Vegeta initially, as stated in the manga, but came from another, unnamed planet. Despite their incredible powers, the Saiyans were primitive and backwards, and lived in small clans scattered across the deserts of Vegeta. Meanwhile, the Tsufurujin used their ingenuity to create large metropoli in which to live, and were fairly prosperous. It was they who originally named their world Planet Plant. Their life was a peaceful one, until suddenly, the Saiyans decided to attack. The Saiyans, led by King Vegeta, declared war against the Tsufurujin. The Saiyans were giants compared to the Tsufurujin; but due to the latter's technology, they managed to keep an upper hand in the war. But then something happened to give the Saiyans an upper hand. The full moon came up, something that only happens once every 100 years (every 8 in one of the English dubs), and the Saiyans possessed the ability to transform into giant apes called Oozaru whenever exposed to the light of a full moon. In their new forms, they easily defeated and obliterated the Tsufurujin and took over the planet, renaming it Vegeta after their king.