When Crota opened a portal in space at the end of Destiny's Books of Sorrow Part 2, it allowed the Vex to invade Oryx's Throne World and the Hive's netherrealm.
The Vex, as machines that aren't able to figure out the Hive's sword logic, are not able to put up a fight. But when the Vex Mind called "Quria, Blade Transform" was created by Vex, it enabled them to deduce how the Hive's world works.
Quria is seen to kill everything it can, so it goes through the portal with the warrior Vex that Crota created.
The Deathsingers Ir Halak and Ir Anûk (Crota's twin sisters) creates an annihilator totem, and uses it to smash the Vex. But Quria is able to lock open the gate that Crota opened, to prevent it from closing. So the Vex and the Hive fight for a hundred years between each other's dimensions.
The invasion was blamed to Savathûn because she tricked Crota into opening the gate that allowed the Vex to get in. But Oryx returns home and destroys all the Vex in his Throne World. Oryx punishes Crota by throwing him into the Vex gate network, as reported by Gamerant news.
Oryx knows that the Vex is a worthy opponent because he cannot completely destroy them. But Oryx comes up with a solution and decides to move his Ascendant realm, his Throne World, and his Court aboard a gigantic spacecraft, a Dreadnaught.
Quria and the Vex forces are unable to defeat Oryx and as he moves through their ranks, he destroys them.
Mozaaf posted that Oryx and the Hive continue to hunt down The Traveler and discover that it visited another solar system called Harmony. When the Traveler left Harmony, it left an object called the Gift Mast, a giant monument that floats above the star system which "sings in radiance." It's not exactly known what it is, but the object is clearly filled with the Light of the Traveler, and Oryx wants to destroy it.