To clear up the storyline of Halo 4. The Covenant that you fight are actually remnants of the old Covenant. They are extremists and believe that Requium is home to their god, a.k.a. the leader of the Prometheans. The Prometheans are of Forerunner design, and how and why they were created is revealed in the campaign. Also, the story is not made up by 343 Industries. They based it off of the books. Just like Bungie did. The books came before the games. Some editing to make it look better, for sure, but they wouldn’t make up stories.