Traveler visited the Fallen first. Advanced them to be able to fight the darkness but they were not strong enough so the Traveler ditched them and found us. Fallen are super pissed their God left them for us so they plan on killing us all to prove themselves to the Traveler. Vex are time traveling machines from either a different dimension or time or both. They worship the darkness like lost puppies bud don't know what it is. Cabal are running from something bigger, probably the actual darkness, not the Taken, so they have run to our solar system because the Traveler repels the darkness somewhat. They are upset that we killed off all the commanders though so they are sending a larger party to investigate what happened. The hive are pretty much another species who decided to give up their will power and bodies to receive unlimited power from the darkness or the dragon people. They are pretty much the darkness that we know so far. Any questions?