Between c.1697—1699, Sauron continued his onslaught of the free peoples of Middle-earth. The survivors of Eregion were too few to stand up to him in battle and so Eregion was therefore abandoned to Sauron while Elrond fled with the few remaining refugees to establish Rivendell.
As for the other half of that wonderful and rare elf-dwarf relationship, the gates of Moria were shut and the area never recovered its former glory. Sauron’s forces ran rampant throughout Eriador, and those that could fled to Rivendell (thus increasing Elrond’s own “forces” at the same time). Although Celebrimbor refused to reveal the locatioin(s) of the Three Rings (before unceremoniously having his corpse converted into a banner for Sauron’s armies) Sauron guessed that they had been hidden in places and with people whom Celebrimbor felt he could trust Gil-galad, Elven King, would have been chief among these trustees. And so it was that Sauron marched upon Lindon, in the hopes to regain at least one (if not more) of the Three.
But, as is so often the case in war, Sauron spread his army too thin. As he marched West upon Gil-galad, he had to leave a significant portion of his forces behind to guard Elrond further back East so as to not be attacked both front and rear. That didn’t stop him from causing all sorts of destruction along the way over the next several years, however. He effectively subdued all of Eriador, not counting Elrond’s forces in Rivendell, and headed for Gil-galad’s doorstep in the havens at Lindon.
Gil-galad was not to be caught at unawares, however. He had long expected such an attack from Sauron and had prepared by sending messages to Númenor seeking aid. Lindon was reinforced by Númenor and thus when it actually came to battle with Gil-galad’s forces, Sauron was actually easily overmatched, his army completely destroyed, and he managed to escape by sheer luck back to Morodor.
Eriador was in ruins. But a long peace followed. Sauron would take a long time to rebuild his forces once more. The White Council held its first gathering/meeting, and Elrond was given one of the Three Elven Rings – Vilya, the Ring of Air, the Blue Ring. The Red Ring, the Ring of Fire, Narya, was held by Gil-galad in Lindon, and Galadriel kept Nenya, the White Ring, the Ring of Water.
And so begins a time of peace in the West of Middle-earth. The Númenóreans established realms along the costs, and things seen to be going well indeed in the Western regions. Sauron therefore turns his attention Eastward, leaving the Westlands and Coastlands for the most part alone. He builds Barad-dûr in Mordor and fortifies its defences. Clearly, Sauron knew his enemy was an exceptionally strong one. He could not attempt to conquer Westward until he built up his forces and his strength.
During this time, the Númenóreans continue to grow from strength to strength, both in Númenor and within Middle-earth. But they began to whisper among themselves that they envied the longevity of the Elves and the eternal, everlasting bliss of the Valar. They felt that they were being punished for past wrongs of their forefathers, whilst the Elves (to their minds) were not being punished. They still had (effectively) immortality, despite having partaken in rebellious activities themselves in years past. The Elves, visiting Númenor from Elvenhome in the West (and bringing gifts of knowledge, craft, lore, etc., to strengthen the Númenóreans) tried to explain that death was not a punishment, nor was “immortality” a gift. These were merely as they were each “meant” to be, as they were in their intentional creation by Eru, The One.
This led to a split amongst the Númenóreans. Those who felt somewhat betrayed and unjustly punished by the West, and those who wished still to remain in good relations with the Elves and the Valar. The former were known as the Kingsmen and the latter as the Elendili or “elf friends”. They attempted to ride a fine line between not betraying their King and yet staying true to their friends and allies. Yet they, too, were troubled by the prospect of death. Although the Kingsmen against the Elves and the Valar, none of the the Númenóreans openly rebelled against the West at this time. But they continued to grow in strength.
Sauron, meanwhile, had been building his forces in the East and the South. But soon those nine mortal men whom he had corrupted with lies, using a Ring of Power with to promise wealth, power, and immortality, utterly faded and became the Ringwraiths. This would have been around the year 2251, more than 500 years since Sauron was defeated at Lindon. With these new, terrifying, and very powerful servants, Sauron’s boldness increases. He begins to build up his own forces on the coasts and to attack the settlements of the Númenóreans.
This is how it more-or-less continued for centuries. Númenor found itself heading toward the peak of its strength, and yet also divided among its own people. There was much open talk of distrust of the Elves, and claims were made that they (the Elves) were merely spies for the Valar. Angered and betrayed, the Elves ceased visiting Númenor, and its decline truly began. Meanwhile, Sauron was becoming more bold in Middle-earth.
Throughout the next few centuries, there were rulers on both sides. For example, Tar-Palantir repented of the ways of the former Kings, and desired greatly to re-establish connectivity with the West (to no avail). It was too little, too late at this point. But eventually, in the year 3255, one came to the throne called Ar-Pharazôn. This was a proud King, and he very little cared for the West. He was the most powerful ruler Númenor had ever seen, and he knew it. And when he learned of Sauron’s continued affrays against the coastlands of Middle-earth, and his setting himself up to rule, Ar-Pharazôn became wrathful. WIth a massive force, he set out from Númenor in 3261 with Sauron set in his sights.
Ar-Pharazôn came to Umbar in the South near Sauron’s forces. And with his golden host he set up camp and sent messengers demanding Sauron come to him. Sauron had heard of the increased might of the Númenóreans, and had even experienced it in his battles along the coasts. But nothing, it would seem, had prepared him for Ar-Pharazôn. Here was a King with forces so great and so powerful, that Sauron knew he could not compete. He didn’t even try. He waved the white flag and surrendered immediately to the King.
As a hostage Sauron was taken back to Númenor. But secretly this was all going to plan. Now Sauron was in the King’s own lands, and his guile was put to malicious and treacherous use which would lead ultimately to the complete and utter ruin of Númenor.