I was reading the book of sorrow grimoire earlier, I would recommend all of you do as well, some of it is interesting. I noticed this excerpt from one of the books. [quote]With his sword Crota cut open a new wound into a new space. In here he thought he would obtain a secret power. Out of this wound poured machines called the Vex. They invaded oryx's throne world.[/quote]. This shows us that the vex are not relative to OUR universe. For those that don't know, hive gods have special dimensions where the only truth is power, and power defines existence. The term Sword Logic is used a lot to describe how the hive got their power. In essence, the more you kill, the stronger you become until the you can bend the universe to your will. I also discovered that the Hive are the ones that forced the traveler to abandon the Fallen. They were once known as the Ammonite, and the hive poisoned their world to attack a single traveler, who was an agent of the Sky. TL;DR: Crota caused the vex in our universe, the Hive ruined the Fallen home world.