War of Wills
From Halopedia, the Halo wiki
The San 'Shyuum Civil War was an internal conflict the arose when some of the San 'Shyuum began to believe that they should enter the Forerunner Dreadnought, a relic which had been crashed on their homeworld. An affront to the other San Shyuum's religion, which believed that the Dreadnought shouldn't be touched, the disagreement sparked a civil war. The conflict ended with those who entered the ship (Known as Refomers) fleeing away from the world on the Dreadnought, while the others (Known as Stoics) stayed behind.[1]