From Halopedia, the Halo wiki
After losing a war with one of Vadam's bitter rivals, Ther's enemies claimed rule over the state and placed 'Vadam and his kin in the cellar jails of Vadam keep, where they were mocked by the invaders and fed scraps to prolong their miserable lives. Many of his honorable brethren killed themselves or each other. After weeks of starvation, Ther became thin enough to squeeze through the bars of his window, scale the cliffs below, and swim downriver to Vadam Valley. For many days he walked, eating vermin and scraps before entering the vast deserts of Yermo. There, he wandered for many years, building strength and hardness, making allies with other wanderers. While their statuses were lower than Ther's, they were willing to fight for him and possessed a will to live no matter the odds.
With his new allies gathered, Ther returned to Vadam and attacked the keep, scaling the walls of the tower and slaying his usurpers. He threw their bodies into the river, which legend had it ran purple with blood for a week. Upon gaining control of the state, he had every inmate of the keep too cowardly to commit suicide executed, and from there rebuilt his family.
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