The Battle of Sunaion was a battle between the Swords of Sanghelios led by Thel 'Vadam, their allies Fireteam Osiris led by Jameson Locke, the last of Jul 'Mdama's Covenant forces, and the Created forces led by the Warden Eternal in the state of Sunaion on the Sangheili homeworld of Sanghelios.
AboutJul Mdama's Covenant was a post-war faction of Covenant remnants that formed soon after the end of the Human-Covenant War. They were led by Jul 'Mdama, a Sangheili who developed a vendetta against humanity and the Swords of Sanghelios after his capture by ONI and the death of his wife. During his escape, 'Mdama discovered an isolated group of Sangheili and exploited their faith in the Covenant religion and his knowledge of Forerunner history to create a large group of dedicated followers, using them to quickly grow to one of the most powerful leaders in the aftermath of the fall of the Covenant.
In the aftermath of the fall of the Covenant, a power vacuum formed that created numerous splinter groups, some with their own ideology and goals, and some, like Jul ‘Mdama’s Covenant, that held many of the same beliefs the original Covenant did. ‘Mdama in particular was particularly adept at using the former Covenant member’s long-held worship for the Forerunners to his advantage, creating a powerful alliance in the first couple years after the end of the Human-Covenant War. While he was not a devout follower of the Covenant religion during its existence, he saw that he could build a large contingent of believers by pretending to be a new prophet. This was largely successful, and by the mid 2550s was one of, if not the most powerful Covenant remnant factions that remained.
The series of events that formed Jul ‘Mdama’s Covenant can be traced to a handful of actions performed by ONI and the UNSC during a period of time when ONI was set on creating as much disruption within the former Covenant species as possible. In the events immediately following the fall of the Covenant, ONI began dealing arms to factions fighting against the rule of Thel ‘Vadam to help seed unrest, primarily to a Sangheili known as Avu Med ‘Telcam. During one of these deals, which would have been considered heresy during the time of the Covenant, ‘Mdama uncovered the lengths to which ‘Telcam would go to get power, but was captured by ONI special operations team Kilo-Five. His time in an ONI detention facility in ONIRF Trevelyan on the Sarcophagus enlightened him even further to the honorless ways humanity fought wars, and when he escaped soon after, took much of that knowledge to heart. That, coupled with the loss of his wife at the hands of Thel ‘Vadam and the UNSC during the Siege of Kolaar, was the spark that lit the fire in Jul ‘Mdama to gain power and fight humanity wherever he could.
Jul ‘Mdama’s Covenant fell even faster than it had grown. In October of 2558, after years of uncovering Forerunner artifacts and using them to build his army, ‘Mdama was killed on Kamchatka by Spartan-IV Fireteam Osiris during the Battle of Kamchatka. His death was a fatal blow to his loyal supporters, though they would hold on for several weeks at the stronghold of Sunaion on Sanghelios until they were finally driven out completely by the Swords of Sanghelios on October 27th.