From Halopedia, the Halo wiki
As the War of Beginnings raged on for decades, the technological superiority of the San'Shyuum's Dreadnought spurred the Sangheili race to utilize Forerunner technology to defend their worlds. As a result of the Sangheili's augmented defenses, the conflict reached a point of stalemate and eventually left both sides open to compromise. In 852 BCE, Breaking Shadow brokered a "tentative truce" with the Sangheili leader Pelahsar the Strident. Both leaders forgave the past crimes of their species and began working to form a harmonious alliance, one that would soon be established by the Writ of Union and become known as the Covenant.
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