Now, if you haven't beaten Halo 4 yet, there may be some spoilers here. So stop reading. OK?
As we learn in Halo 4, the Forerunners and Humans already made contact millenna ago and a war broke out. The Forerunners put us essentially back into the Stone Age. Now here's my question; is this something Bungie had already established in the Halo universe or is this something 343 added? I'm really sorry if this is a silly question, I don't know as much about Halo's overall storyline as I'd like to.
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It was implied in Halo 3 if you were paying very close attention, but you wouldn't have caught onto it unless you'd read Cryptum. So 343i effectively made the idea, but Bungie planted the seed. Edit: Basically what ajw said. [Edited on 12.04.2012 1:23 PM PST]