The Silmarillion

Men proved easier to ensnare. Those who used the Nine Rings became mighty in their day, kings, sorcerers, and warriors of old. They obtained glory and great wealth, yet it turned to their undoing. They had, as it seemed, unending life, yet life became unendurable to them. They could walk, if they would, unseen by all eyes in this world beneath the sun, and they could see things in worlds invisible to mortal men; but too often they beheld only the phantoms and delusions of Sauron. And one by one, sooner or later, according to their native strength and to the good or evil of their wills in the beginning, they fell under the thraldom of the ring that they bore and under the domination of the One, which was Sauron's. And they became for ever invisible save to him that wore the Ruling Ring, and they entered into the realm of shadows. The Nazgûl were they, the Ringwraiths, the Enemy's most terrible servants; darkness went with them, and they cried with the voices of death.

Now Sauron's lust and pride increased, until he knew no bounds, and he determined to make himself master of all things in Middle-earth, and to destroy the Elves, and to compass, if he might, the downfall of Númenor. He brooked no freedom nor any rivalry, and he named himself Lord of the Earth. A mask he still could wear so that if he wished he might deceive the eyes of Men, seeming to them wise and fair. But he ruled rather by force and fear, if they might avail; and those who perceived his shadow spreading over the world called him the Dark Lord and named him the Enemy; and he gathered again under his government all the evil things of the days of Morgoth that remained on earth or beneath it, and the Orcs were at his command and multiplied like flies. Thus the Black Years began, which the Elves call the Days of Flight. In that time many of the Elves of Middle-earth fled to Lindon and thence over the seas never to return; and many were destroyed by Sauron and his servants. But in Lindon Gil-galad still maintained his power, and Sauron dared not as yet to pass the Mountains of Ered Luin nor to assail the Havens; and Gil-galad was aided by the Númenóreans. Elsewhere Sauron reigned, and those who would be free took refuge in the fastnesses of wood and mountain, and ever fear pursued them. In the east and south well nigh all Men were under his dominion, and they grew strong in those days and built many towns and walls of stone, and they were numerous and fierce in war and aimed with iron. To them Sauron was both king and god; and they feared him exceedingly, for he surrounded his abode with fire.

Yet there came at length a stay in the onslaught of Sauron upon the westlands. For, as is told in tile Akallabêth, he was challenged by the might of Númenor. So great was the power and splendour of the Númenóreans in the noontide of their realm that the servants of Sauron would not withstand them, and hoping to accomplish by cunning what he could not achieve by force, he left Middle-earth for a while and went to Númenor as a hostage of Tar-Calion the King. And there he abode, until at the last by his craft he had corrupted the hearts of most of that people, and set them at war with the Valar, and so compassed their ruin, as he had long desired. But that ruin was more terrible than Sauron had foreseen, for he had forgotten the might of the Lords of the West in their anger. The world was broken, and the land was swallowed up, and the seas rose over it, and Sauron himself went down into the abyss. But his spirit arose and fled back on a dark wind to Middle-earth, seeking a home. There he found that the power of Gil-galad had grown great in the years of his absence, and it was spread now over wide regions of the north and west, and had passed beyond the Misty Mountains and the Great River even to the borders of Greenwood the Great, and was drawing nigh to the strong places where once he had dwelt secure. Then Sauron withdrew to his fortress in the Black Land and meditated war.

In that time those of the Númenóreans who were saved from destruction fled eastward, as is told in the Akallabêth. The chief of these were Elendil the Tall and his sons, Isildur and Anárion. Kinsmen of the King they were, descendants of Elros, but they had been unwilling to listen to Sauron, and had refused to make war on the Lords of the West. Manning their ships with all who remained faithful they forsook the land of Númenor ere ruin came upon it. They were mighty men and their ships were strong and tall, but the tempests overtook them, and they were borne aloft on hills of water even to the clouds, and they descended upon Middle-earth like birds of the storm.