So I was doing some thinking regarding our enemies. I think their may be an alliance between the vex and the hive, and may be an alliance between the Cabal and the Fallen. The reasoning for my argument is that you don't encounter the hive and the vex on the same the planet. They are both ritualistic societies and are both found worshiping forms of the darkness. Again, they don't occupy the same planet. The Hive have the Earth and the Moon. The Vex have Venus and Mars. They don't overlap each other. Same thing with the Cabal and the Fallen. Both seem to be secular societies and have clear leaders they answer too, not figures they worship, unlike the Hive and Crota. The Fallen have their Kell and the Cabal have their commanders. The Fallen have Earth, the Moon, & Venus. While the Cabal only occupy Mars. If the Cabal are some huge militaristic society, than they should have the means to launch forays into the other planets for resources, or for the sheer conquest, which militaristic societies are known for, i.e. the Roman Empire, Sparta, etc. But the Cabal haven't done that. Which could be indicative of an alliance with the Fallen. For all I know, the next DLC would throw all that to the crapper. That's just my two cents. EDIT (did some more thinking): Also the Fallen, according to the Grimoire, are scavengers that want and steal technology. So why wouldn't the Fallen be on Mars by the thousands? Mars has Freehold "which gave birth to technological wonders," so why wouldn't the fallen want that treasure trove? Because during the agreement, now this is pure conjecture at this point, it could have been agreed upon that since Mars has such great technology, it could be viewed as having equal weight to the human's other three worlds, Earth, Venus, the Moon. Even though Earth is our home world. Mars had the Traveler on it during the "Golden Age" so it could be said that Mars is/was strategically more important, than even Earth, because of the technology being born there. Hence why it would make sense that their is an alliance between the Cabal and the Fallen. The argument is less certain for the Hive and Vex because they could view each other as heretics to each other's religion. But since they don't occupy the same planet, or the small areas of the planet we have access too, I think their could be an alliance.