In the aftermath of the collapse of the Covenant, the Sangheili found themselves in political, military, and religious turmoil. Having long depended on the San'Shyuum for political leadership, the Sangheili found that they lacked any form of political organization beyond their traditional feudal states. While Arbiter Thel 'Vadam began the process of forming a new government to lead Sanghelios and its various colonies, many kaidons began hoarding ships and weapons for their own agendas.
Additionally, while most Sangheili renounced the Great Journey, many did not wholly abandon worship of the Forerunners. As a result of this, the Servants of the Abiding Truth, an ancient order of monks, began preaching a return to the Sangheili's ancient ways of worshiping Forerunner artifacts. Consequently, they felt that Thel 'Vadam and those loyal to him were committing blasphemy by saying otherwise. Avu Med 'Telcam, a former Field Master, began recruiting dissident Sangheili into a force to rise up against the Arbiter's followers.
Admiral Margaret Parangosky, of the Office of Naval Intelligence, believed that keeping the Sangheili mired in internal dissent would leave them unable to threaten the weakened UNSC. This opinion contrasted with that of most of the Unified Earth Government, which believed a peace treaty was desirable. ONI took advantage of the Sangheili's unstable political situation, attempting to keep the Sangheili splintered and disorganized by inciting the Servants of the Abiding Truth to rebel against 'Vadam. ONI's aid allowed the Servants of the Abiding Truth to amass enough weapons to begin an all-out insurrection against 'Vadam and his allies in early 2553.
Jul 'Mdama, a former member of the Servants of the Abiding Truth, eventually formed his own revival of the Covenant, with the Sangheili again serving as its leadership caste after learning of ONI's alliance with the Servants of the Abiding Truth.
Opening of hostilities
Following the end of the Human-Covenant War in March 2553, an attempted Jiralhanae insurrection in Ontom led Avu Med 'Telcam, leader of the Servants of the Abiding Truth, to the decision for an immediate assault on the state of Vadam. Along with nine ships and forces from Nuan keep and Rtova keep, 'Telcam commanded the assault from the frigate Unflinching Resolve. Eventually, however, the Unflinching Resolve suffered a direct hit and crash landed. Despite being caught off-guard it appeared as though the Arbiter would be victorious, however, news spread that he allowed humans to land on Sanghelios; this caused many keeps to ally with the Servants of Abiding Truth and the tide turned in their favor. The Arbiter was caught off guard and when his own reinforcements couldn't arrive on time, he reluctantly accepted Admiral Terrence Hood's offer for help in fending off the attackers. The tide turned when the UNSC's new flagship, Infinity, arrived over Sanghelios and destroyed the rebel destroyer Defender of Faith before finishing off the rebel ground forces with a MAC round. The UNSC Port Stanley, posed as a Kig-Yar pirate ship, destroyed a few of 'Vadam's ships in order to maintain the stalemate between the two factions, granting the Arbiter a Pyrrhic victory.
After the battle 'Vadam entered talks to board Infinity. The remnants of the Servants of the Abiding Truth escaped to New Llanelli to regroup. One month later 'Telcam said he would remain on New Llanelli until he convinced more keeps to join his cause or obtained enough ships to destroy those who refuse.
However, the conflicts in Vadam led to other engagements throughout Sanghelios.
Massacre at Nes'alun keep
Unlike the majority of keeps in Acroli, Nes'alun keep was against the Arbiter. While the keep's males left to fight Vadam's forces, the keep females and children were left behind. The elder of Lacalu keep took advantage of this and attempted to seize the keep and its land. The keep's lady, Elar 'Nas, defended the other females and children in a small farmhouse for an unknown length of time. Soon the keep's Unggoy laborers Dengo and Gikak returned along with Evan Phillips, who had been teleported to the nearby Forerunner ruins. Elar allowed Phillips to come inside, armed him, and prepared themselves for another wave of attackers.
Soon afterwards Kilo-Five arrived at the keep to retrieve Phillips. Their extraction was stalled when the Tart-Cart, piloted by Lian Devereaux, was attacked by several Type-26 Banshees. After holding off more Lacalu warriors, Vasily Beloi, Malcolm Geffen, and Naomi-010 extracted Phillips in the midst of battle, leaving the women and children to defend for themselves. Elar and her clan were later killed which unsettled Phillips.
Other fighting and the Swords of Sanghelios
Over the next few months, unrest on Sanghelios was put down though off and on fighting would continue for years and include a number of Sangheili worlds.
In October 2558, the increasing threat of the rogue AI Cortana caused Doctor Catherine Halsey, who was working with Jul 'Mdama, to secretly reveal his location on the remote Forerunner world of Kamchatka to the UNSC. As Jul 'Mdama's Covenant battled against his rebelling Promethean forces, Fireteam Osiris made their way to the location where 'Mdama and Halsey were attempting to access the Forerunner Domain. In the battle that followed, 'Mdama was killed by Spartan Jameson Locke with his combat knife after a brief fight between the two.
'Vadam's failed assassination attempt
On October 27, 2558, the remnants of Jul 'Mdama's Covenant attacked the Elder Council Chamber in Nuusra on Sanghelios in an attempt to kill Thel 'Vadam. At the same time, due to the need to find Blue Team, Fireteam Osiris was sent to Sanghelios to enlist Thel's help to use the Forerunner Guardian on the planet to follow Blue Team. Arriving as the attack was underway, Osiris aided the Swords of Sanghelios in repelling the attack and rescued Thel.
In order to access the Guardian, Doctor Catherine Halsey came up with a plan to retrieve a Forerunner Constructor from a support facility nearby. As Osiris fought to reach the facility, the Swords of Sanghelios battled against the remaining Covenant forces in the area, including a Kraken walker. Osiris destroyed the Kraken, ending the battle with the Covenant forces in Nuusra and leaving Sunaion as their last stronghold.
Battle of Sunaion
After Halsey succeeded in programing the Constructor, the Swords of Sanghelios, aided by Fireteam Osiris, launched an attack on Jul 'Mdama's Covenant's final stronghold in the city of Sunaion. Osiris aided Thel's forces in clearing out the anti-air defenses so that Thel's ships could move in and fought their way through the city to reach the Guardian before it could launch. With the help of Halsey and Sarah Palmer, Osiris succeeded in boarding the Guardian before it launched into slipspace though they had to face Prometheans and the Warden Eternal first. Having previously witnessed the launch of a Guardian, Locke warned Thel to move his ships back as the construct would release a series of concussive blasts before making the jump. As a result, 'Mdama's Covenant would take the brunt of the blasts instead which could be used by the Swords to their advantage. This tactic succeeded with much of 'Mdama's Covenant's ships knocked out by the final blast as the Guardian jumped to Genesis.
With the Prometheans and Guardian gone and the Covenant forces devastated, Thel had his warriors hunt the survivors to the last, bringing a final end to Jul 'Mdama's Covenant.
Second Onyx conflict
List of appearances