Sargeras returned to the Titans and informed them of the Void Lord’s plans. Sargeras cleaved the planet in two, destroying the Old Gods and the Titan. They sought to turn a sleeping Titan into an ultimate being under their control that could wipe out all existence. By capturing some Nathrezim that were serving the Old Gods and torturing them, he learned the Void Lords’ plans. He found that the Titan at its heart had become corrupted too. While Sargeras was exploring the worlds he came across one that had been corrupted by the Old Gods. The dark creatures that they hurtled throughout the universe would become known as the Old Gods. Once found, the Void Lords would try to corrupt the Titan while it grew and slept. They combined all their power and sent forth dark creatures throughout the universe to find a world with a Titan inside it. The Void Lords found that the Titans were beyond their ability to control and thus came up with a plan. They could, however, warp reality and twist living beings to their will.
Only the most powerful could manifest themselves in the physical universe and this only happened for a short time. They lived outside the physical universe and sought to consume all matter. While Sargeras was fighting the demons, he learned of a darker power, the Void Lords.
Sargeras was the champion of the Titans and spent much of his time fighting the demons of the Twisting Nether. Before the Burning Legion there were just demons coming forth from the Twisting Nether to wage war on worlds.