From Halopedia, the Halo wiki
Green Hills was attacked and glassed by the Covenant in 2525, becoming one of the first human colonies to be lost after the attack on Harvest at the start of the Human-Covenant War.[Note 1] Initially, the United Nations Space Command hoped to cover up the loss by implicating rebels causing communications blackouts. However, they were soon forced to reveal that the UNSC was now at war with a xenocidal alien empire; the Covenant had killed two million civilians by glassing Green Hills and Second Base.
Spartan John-117 fought alongside an unidentified Orbital Drop Shock Trooper on Green Hills. The two were briefly reunited in 2557 during the Battle of Requiem, the former Marine having since become a Spartan-IV.
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