From Halopedia, the Halo wiki
- The Reformist San'Shyuum first encounter the Sangheili on their frontier world of Ulgethon. The San'Shyuum send a delegation to explain that they worship the Forerunners like the Sangheili. However, like the San'Shyuum Stoics, the Sangheili believe that Forerunner relics are not to be modified in any way and view the San'Shyuum's reverse-engineering of the artifacts as grave blasphemy. Led by an Arbiter, the Sangheili resist the San'Shyuum's entreatment and summarily executed the delegation, sparking the War of Beginnings.