I wouldn't say they're "required", but Guardians of the Galaxy does spin out of them. The Guardians form as a direct result of both of those events. But the dialog does convey pretty much all information that's absolutely needed. "The galaxy is in a weakened state due to X and Y." That sort of thing.
I read Guardians first though (and then back-filled with Annihilation and Annihilation: Conquest), and I managed ok. You can find decent recaps online.