It shouldn't really be surprising that the Darkness can potentially bend reality; look at what it's "ancient enemy" the Traveler can do. The other races make me curious though. My theory is that the Fallen survived an encounter with the Darkness and now chase it across the stars to scavenge the civilizations it destroys. The Cabal aren't connected to at the Darkness all; they're just expansionist Space Romans who see Sol as their next conquest. The Hive are clearly creations/worshipers of the Darkness, and the only enemy race with an obvious direct connection. The Vex are still wrapped in mystery.