[Halo 4 story explanation]

The forerunner war is a retcon and it kind of sucks. The rest of the problems are poor writing and it does not make a lot of sense. The Didac and Captain of the infinity are nothing more than plot devices to extend the length of the real story which is saving Cortana. They both have to do totally stupid things and act like idiots in order to extend the plot. But that's only my opinion and some people really like the story. Then again some people think the Twilight series is brilliant writing. It's all about taste in most cases. For me this game was style over substance, I don't generally let plot wholes, plot devices or idiot plots slide, but some people do and they like the story for emotional context, and themes. I prefer a tighter story.

hey dipwad, take 5 seconds of your life to confirm facts before sounding like a total ******.

So here's a brief rundown of the war(in bad grammar).

100,000 years ago

Flood attack human and san shyumm (prophets).

Human & prophet form alliance and in other escape flood evacuate their infected planets and take over planets occupied by lower species.

Forerunners consider this an affront to mantle (they unaware of flood) and start war with human-prophet alliance.

Human-prophet find a cure to flood, flood driven off, but the alliance gets destroyed by forerunners, cure to flood lost.

Flood comes back and proceeds to rape forerunners. Forerunners destroy all life including themselves.

The end.