From Halopedia, the Halo wiki
Far Isle was a human colony planet, within Unified Earth Government space. The colony was the site of what is considered to be one of the United Nations Space Command's worst atrocities; in response to a rebellion in 2492 that they were unable to quell, the UNSC razed the colony using nuclear weapons, leaving no survivors.
Far Isle was colonised some time before 2492.
In 2492, amidst unprecedented levels of tension and civil unrest throughout UEG space, a civilian revolt broke out on the planet. The United Nations Space Command was unable to contain the rebellion, and resorted to using nuclear weapons to raze the whole colony. Code: BANDERSNATCH was declared in the aftermath, indicating a major radiological- or energy-based disaster, and the colony's populace was reportedly completely wiped out.
The colony's destruction led to multiple other rebellions elsewhere. Although the Callisto Incident is widely accepted to have been the event that finally ignited the tensions across the colonies and caused the Insurrection, the destruction of Far Isle was also acknowledged as a potential cause. Even as late as 2553, the UNSC's handling of the colony's rebellion remained a driving force for the hatred that many in staunchly independent colonies such as Venezia held for the UNSC and UEG.
The nuclear bombardment of Far Isle likely appears in the Halo Legends episode Origins II, when Cortana discusses the Insurrection. A flight of GA-TL1 Longswords is shown dropping bombs on a coastal city; in the next shot, a burning, slagged crater is shown in the middle of the city.
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