Maybe Precursors,One. Because the Forerunners are extinct, two. The Flood have been eliminated but don't take my answer seriously its just an opinion and correct me if I'm wrong.<- precursors are extinct too
^ Always thought the forerunners were in another galaxy since they are tier 0? ~Tim~ <-- no but they could have made it to one
No the Precursors are tier 0, the forerunners are only tier 1, the forerunners were wiped out. it is possible that precursors did leave the galaxy and finally returned and there might still be samples of the flood left on the remaining undescovered halo rings (or other forerunner installations.) but the construct in the halo 4 trailer certainly isn't flood or forerunner so it is my opinion that the construct is actually prehistoric human. (if you read halo: cryptum, you'll understand.)
Forerunners weren´t completely wiped out. Some of them survived and fled the galaxy.
maybe both. :O
^ Thanks for the clarification :) ~Tim~
What about the remainders of the covenant. they are beaten but... several prophets live on, ready to lead a new covenant and hardly surprisingly kill humans
^ The remaining covenant are completely smashed, this is because gravemind wiped out High Charity and we know from books and other sources that the covvy got even weaker in decades after the events of halo 3. Without the elites the covenant are weak due to Elites the remarkable "tactical adeptness". The Brute's "tactical helplessness" can be heard in a radio transmission during the battle of 00, saying "No! Shoot the Carrier!", the elites beat the brutes (with a lil help of the UNSC) above The Ark 3 to 1. so if the elites somehow go back to the covvy then halo 4 will have them if not, well they wont. ~Tim~