I'm going to start this topic by explaining that I have very little to no evidence to support my theory/hypothesis, so go into this knowing that it is primarily speculation. That being said, let's start with what we know. We know that the Traveller zips across the cosmo, assisting and helping to develop celestial bodies and the communities and civilizations that inhabit them, essentially serving as a performance enhancing drug for whatever society it may bless with it's presence. We know that it was first found by people, on Mars, and was then taken (or moved of it's own free will?) to Earth. Perhaps being on the planet, the Traveller was able to Teraform Mars, and allow Humans to inhabit it, perhaps we already knew how and it just happened to be there, idk, but I'm getting off topic. So for whatever reason we find ourselves defending the Traveller from 4 different enemies, or what we are collectively calling 'the darkness.' So here's my core theory... What if the enemies we are fighting, were all former recipients of the Traveller? Who had all grown to depend on it for survival, or thrival (is that a word?). Like, for the Fallen, perhaps they needed the Fallen to supply them with precious ether when they began to run low, and then out of nowhere it split off into the cosmos, leaving them angry, bitter, and desperate, and [i]in[/i] their bitterness, they decided that in the best interests of their survival, they would hunt down the Traveller. With the Cabal, they may have grown to see the Traveller as their ultimate weapon, and core method for defeating armies and annexing planets, as if a society doesn't have to worry about their survival and general well-being, they can focus their efforts on their military, and create an empire of sorts. But once the Traveller left, the Cabal would find themselves struggling to maintain a dominant presence across the cosmos while also trying to relearn how to provide for themselves, and in their desperation, forcing expansion [i]even[/i] further, finding themselves in [i]our[/i] neck of the woods. With the Hive, they likely worshipped the traveller, but manipulated it's light into something dark and sinister, growing their might through attrition of other races or societies, killing, salvaging, and consuming the meat, blood, and marrow of even the weakest organisms in order to further their power. Once the Traveller left however, they would hunt it down with great zeal, seeking...no, [i]needing[/i] to twist it's light into their arcane dark energy, their lifeblood that they use to feed and grow their armies, and they too would find themselves in our space, taking pieces for the traveller. And with the Vex, I have a somewhat different theory. Perhaps our Traveller was not always the only one, and perhaps, the 'Black heart' was once, or still is, an old Traveller. Perhaps the use and intent of the recipients of the Traveller's light, can influence the Traveller, and may perhaps poison or infect it with the greed or bloodlust of the society (like with the stolen Traveller shard found on the moon). However with their Traveller (Black heart) dying, the Vex would be getting closer and closer to moving in to take our's as a replacement, or possibly even to destroy our's to preserve the power and exclusiveness of their own Traveller. With their race being the oldest, it would make sense why and how their traveller could be so tainted, worn, and used up, and how they could have become so much more powerful, having been absorbing the light and being gifted the power for far longer than any other race, and perhaps further still, their Traveller never wanted this fate, and was trying to seek out [i]our[/i] Travelller in order to perhaps heal itself and cure it of it's...how might you say...Vexually transmitted disease? Feel free to point out the holes and issues with my theory, shoot it down or vote it up, comment, expand with your own thoughts, and just generally discuss. I just had to get this whole thing off my chest before the idea slipped my mind...