User blog comment:B1littlehero/Speculation of the Origin of Species/@comment-7622429-20140611002324

Well, the only sure thing is that the Traveler came to this solar system from very far away, as did the Darkness. We know the Hive get their own powers from the Darkness, in a similar manner to how the Traveler gave the Guardians theirs. The Cabal and Fallen seem to be more independent races, and not really affiliated with the Darkness. They seem like the average space-faring races, with the Cabal having a lot more structure and order, but the Fallen having a greater presence throughout the system due to the race's nomadic lifestyle.

The Vex could be affiliated with the Darkness, since they don't seem to cooperate with ANYONE, and in fact could be the more futuristic army of the Darkness, with the Hive being the ancient one. The Cabal and the Fallen could possibly be more of "guns for hire" by the Darkness, not specifically used by it, but they're more than willing to do it if it means taking out Humanity. Though, the inter-species quarreling of these groups likely stems from the Cabal and Fallen not being specifically tied to the Darkness, since they do have their own interests.