From Halopedia, the Halo wiki
The Kradal conflicts, sometimes known collectively as the Kradal conflict, were a series of bloody Forerunner civil wars that took place in the galactic center at some point before the human-Forerunner war. Bitterness-of-the-Vanquished commanded Warrior-Servant forces during these conflicts, which saw the loss of countless warriors. The Z-130 Suppressor was first used during the Kradal conflicts. A stone monument was later erected in the memory of the conflicts.
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