Sauron stood between the veil of existence. Beaten by mere mortals, a hobbit no less. His dark form shimmered for a moment with the force of his rage. He considered passing on into the void into eternal nothingness, but then again, an eternity with his master, Morgoth, was a most unpleasant prospect. So he waited, seeking inspiration from the darkness. His thoughts stretched to the four corners of Arda as he searched for some tangible detail he could pursue. He looked for many weeks but searched in vain as this world was purged of evil in his departure.
Suddenly, Sauron realized that this was the answer. This world lacked any means for him to re establish his rule. However he soon became aware of another land which drew his interest. So he sent his spies to find more of this world, and at last he found his weapon with which to dominate Arda. Long ago, the maiden spirit Arien, spirit of the sun, had cried a single tear from the heavens. This tear landed near a small kingdom named Corona where it grew into a flower of life.
This flower was given the power of Arien's master, Vána the Ever-young. It was a flower of healing. "Destroyed", Sauron thought grimly. the flower was used to save a mortal queen as she lay dying with a child. But wait, within this queen the magic settled into a girl. Although her power was diminished, he could still feel the thrum of its energy within her. If he could get his hands on this girl… He could resurrect himself and his servants and reclaim dominion over Arda and possibly this land as well. Sauron had only to send a representative over to Corona and take this girl to cover all of creation in a great darkness.
Calling all manner of evil to him, Sauron brought the horrors of the void under his thrall: taking servants both new and old.
So Sauron ripped the veil of the two worlds and began to assemble his forces to enter Corona. Members of Arda would slowly find themselves appearing in Corona and this could be a problem. Thus Sauron made haste as his forces assembled for war…