The Blooding Years, also known as the Sangheili Civil War, was an armed conflict between the Swords of Sanghelios and different factions opposed to the Arbiter's rule.
The seeds of the Sangheili Civil War began immediately after the end of the Great Schism and the Human-Covenant war. In January 2553, the ArbiterThel 'Vadam began to visit the various states to propose a peace treaty with humanity. He argued that too many Sangheili had been lost in the Great Schism, and that Sanghelios had to be rebuilt. This proposal was not well received by all, and civil unrest ensued. Dissident Sangheili began to join the Servants of the Abiding Truth, an old orthodox religious group who opposed the Arbiter led by Avu Med 'Telcam.
In February 2553, Fleet Admiral Terrence Hood arrived on Sanghelios to formalize the cease-fire with the Arbiter. They met in the state of Vadam and formally ended hostilities, solidifying the Treaty of 2552.
After a Jiralhanae rebellion began in Ontom, the Servants of Abiding Truth decided it was the time to strike against the State of Vadam. This assault was met with massive resistance including forces from the Swords of Sanghelios and the UNSC Infinity. The attack would ultimately fail with the Servants eventually retreating to New Llanelli.