In Halo 2, the Flood had already been unleashed against the Sentinels since the firing of the Halos 100,000 years ago. See http://halo.wikia.com/wiki/Flood ("Flood" on Halopedia, the Halo Wikia) and also the chapter name "100,000 Years War" on the last chapter of Sacred Icon, one of the H2 campaign levels. =]

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RelentlessRecusant

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RelentlessRecusant
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