Hostile Covenant?

Games Other Halo
1

I didnt read the books, so my data might be off.

At the end of halo 3 the humans and covenant had a truce to kill a common enemy. Halo 4 takes place 4 years after the events of halo 3. So I pose this question, what happened in those four years that caused the humans or covenant to break the truce?

2

Elite civil war/Splinter factions are implied from Glasslands, though nothing is definite so far into the books in that regard.