Does anyone that read the books know why the elites are against humans again? And what happened to the brutes? I know Cortana said, “A lot can happen in 4 years”, but I’m curious as to what happened. In Halo 2 the Elites left the covenant because of the prophets choosing brutes over them and betraying them. Did they just join back? If you think you know why, please give it a shot because it’s driving me nuts XD
Right now the Elites you see in Halo four are pretty much a terrorist cell know as the Storm. They arent an actual part of the Covanent.
TL;DR version:
Two factions of Elites. Those that Follow Arby and Human friendly. Those that still believe Forerunner are gods and hate humans.
Just like the other covenant races, some Elites still worship the Forerunners and hate humanity. Not sure what the ratio is, but I assumed the majority of Elites are still allied with us.
Brutes went back to their original way of life “infighting” and all that jazz. Along with losing a good amount in the end of the wars. Basically they went to being a non threat.
They heard that the Didact wanted to go after the humans.
They decided that was good enough of a reason to go after the humans as well.
Thanks guys 
makes so much more sense now. I really do hope that they show the Arbiter somewhere in Spartan Ops though XD