The island was brought up from the sea as a gift from the Valar to the Edain, the Fathers of Men who had stood with the Elves of Beleriand against Morgoth in the War of the Jewels. Númenor was meant to be a "rest after the war" for the Edain. Early in the Second Age the greater part of those Edain that survived their defeat from Morgoth journeyed to the isle, sailing in ships provided and steered by the Elves. The migration took fifty years and brought 5,000 to 10,000 men, women and children.
The realm was officially established in S.A. 32, and Elros Half-elven, son of Eärendil, and brother of Elrond and descendant of all the royal houses of Elves and Edain, became the first King of Númenor. Under his rule, and those of his descendants, the Númenóreans rose to become a powerful people. The first ships sailed from Númenor to Middle-earth in the year 600 of the Second Age.
The Númenóreans were forbidden by the Valar from sailing so far westward that Númenor was no longer visible, for fear that they would come upon the Undying Lands, to which Men could not come. For a long time, Númenor remained friendly with the Elves, both of Eressëa and of Middle-earth, and between S.A. 1693-1700, they assisted Gil-galad in the War of the Elves and Sauron, which broke out after the forging of the Great Rings, in particular the One Ring. King Tar-Minastir and the forces of Númenor were without peer in war, and together with the Elves, they were able to temporarily defeat Sauron. Over time the Númenóreans became jealous of the Elves for their immortality, and began to resent the Ban of the Valar and to rebel against their authority, seeking the everlasting life that they believed was begrudged them. They tried to compensate for this by going eastward and colonizing large parts of Middle-earth, first in a friendly manner, but later as cruel tyrants. Soon the Númenóreans came to rule a great coastal empire that had no rival. Few (the "Faithful") remained loyal to the Valar and friendly to the Elves.
In the year 3255 of the Second Age, the 25th king, Ar-Pharazôn, sailed to Middle-earth and landed at Umbar. Seeing the might of Númenor, Sauron's armies fled and Sauron surrendered without a fight. He was brought back to Númenor as a prisoner but he soon became an advisor to the king and promised the Númenóreans eternal life if they worshipped Melkor. With Sauron as his advisor, Ar-Pharazôn had a 500-foot (150 m) tall temple to Melkor erected, in which he offered human sacrifices to Melkor (those selected to be sacrificed were Elendili, Númenóreans who were still faithful to the Elves).
During this time, the White Tree Nimloth, which stood before the King's House in Armenelos and whose fate was said to be tied to the line of kings, was chopped down and burned as a sacrifice to Melkor at Sauron's direction. Isildur, heroically and at great personal risk, rescued a fruit of the tree which became an ancestor of the White Tree of Gondor, preserving the ancient line of trees.
Prompted by Sauron and fearing old age and death, Ar-Pharazôn built a great armada and set sail into the West to make war upon the Valar and seize the Undying Lands, and by so doing achieve immortality. Sauron remained behind. This force was quoted by Tolkien as the 'greatest force ever assembled on Arda'. In the year 3319 of the Second Age, Ar-Pharazôn landed on the shores of Aman. As the Valar were forbidden to take direct action against Men, Manwë, chief of the Valar, called upon Eru. The Undying Lands were removed from the world forever, and the formerly flat Earth was made into a globe. Númenor was overwhelmed in the cataclysm and sank beneath the sea, killing its inhabitants, including the body of Sauron who was thereby robbed of his ability to assume fair and charming forms, forever appearing in the form of a Dark Lord thereafter.
Elendil, son of the leader of the Faithful during the reign of Ar-Pharazôn, his sons and his followers had foreseen the disaster that was to befall Númenor, and they had set sail in nine ships before the island fell. They landed in Middle-earth and founded the kingdoms of Arnor and Gondor.
The Witch-king and the other Nazgūl rode from Mordor and Dol Guldur searching for the Shire. Four entered the Shire, and found that "Baggins" had moved to Buckland. Several Nazgūl attacked Gandalf onWeathertop and tried to ambush Frodo Baggins in Buckland and at Bree. Five, including the Witch-king, finally found Frodo on Weathertop with the other hobbits, accompanied by the Ranger Aragorn. The Ringwraiths attacked the party, and the Witch-king wounded Frodo with a Morgul-blade. Frodo's wound threatened to turn him into a wraith under the control of the Nazgūl.
As the company made for Rivendell, the realm of Elrond Half-elven, they met Glorfindel, who loaned Frodo his horse Asfaloth. Pursued by all nine Nazgūl, the horse carried Frodo across the River Bruinen. From the far bank Frodo defied the Nazgūl. When the Witch-king rode into the water, Elrond, who controlled the river, released a flood that caught three Nazgūl and their horses. Glorfindel advanced and drove the terrified horses of the remaining Nazgūl into the flood. The horses drowned, and all nine Nazgūl were swept away.
The three commanders agreed that the Goblins and Wargs were the enemies of all, and previous grievances between them were put on hold in face of the greater threat. They arranged their forces on the two spurs of the Mountain that lined the valley leading to the now-sealed off great gate; the only entrance to the Mountain. The Dwarves and Lake-men formed up on one spur and the Elves on the other, while a light rear-guard lined across the mouth of the valley to lure the Goblins between the two, and thus destroy them. Bilbo Baggins, while invisible due to the Ring, tried to sit out the battle on the spur held by the Elves.
Soon the Goblins and Wargs arrived (and now four armies were on the field), and at first the plan worked: they were lured into the choke point and took heavy losses. However, due to their superior numbers, the allied Free Folk did not hold the advantage long. The second wave was even worse than the first, and now many Goblins scaled the mountain from the opposite side, and began to attack the arrayed forces from above and behind, as the main wave pressed forward. The battle raged across the Mountain, and then a great noise was heard: Thorin and his twelve Dwarf companions inside the mountain had thrown down the stone wall they had erected across the mouth of the gates, killing many Goblins. Thorin and Company then charged out to join the battle, covered from head to toe in the finest armour and weapons contained in the treasure hoard of Erebor. Thorin advanced through the Goblins ranks all the way up to the gigantic Goblins that formed the Bodyguard of Bolg, whom he could not get past. The battle degenerated into a chaotic close quarters melee, no quarter asked or given.
As the battle was turning fully against the Free Folk, a number of Giant Eagles of the Misty Mountains arrived (the fifth army), led by Gwaihir, Lord of the Eagles. Bilbo was the first to spot their entrance on the scene and began shouting that "the Eagles are coming!", a shout that was then continued among the other troops of the Free Folk. At this point Bilbo was knocked in the head by a large stone thrown by a Goblin from above on the Mountain, and he passed out. With the support of the Giant Eagles, the battle turned back against the Goblins. Then Beorn himself arrived at the battle, apparently having heard news that a large army of Goblins was on the move. This time he did not appear in his former shape of a giant Man, but had changed his skin to that of a gigantic bear. Beorn drove through the Goblin lines, but paused to carry the wounded Thorin out of the battle. Beorn then returned to the battle with even greater wrath and smashed the ranks of the Bodyguard of Bolg, ultimately killing Bolg himself. The Goblins eventually panicked and scattered, to be picked off by hunting forces from the victors later; many of the Goblin survivors died in the Mirkwood forest.
After twenty-eight years of imprisonment and the death of his children, Húrin was released by Morgoth. "He had grown grim to look upon: his hair and beard were white and long, but there was a fell light in his eyes. He walked unbowed, and yet carried a great black staff; but he was girt with a sword." He was brought to his old homelands in Hithlum, but the Easterlings living there at first did not recognize him and later feared him, believing he served their evil lord Morgoth. The House of Hador had been destroyed, and those who remained as slaves or outlaws held him in suspicion and fear.
Seven outlaws under Asgon joined Húrin, and together they went to the Vale of Sirion. Húrin abandoned his followers and sought the entrance to Gondolin, but the Hidden City was closed, and Turgon at first did not wish to allow him in. Húrin cried out against Turgon, thus revealing the location of Gondolin to Morgoth's spies, and then left. Only after he had left did Turgon have a change of heart and send Eagles to fetch him, but they came too late and did not find him.
Húrin continued to the forest of Brethil where his son and daughter had died, and met his wife Morwen there at their grave at Cabed-en-Aras, just before she, too, died. In anger and despair he sought out the Folk of Haleth, blaming them for the death of his wife and children, and caused a revolt that killed the last Haladin. For Hardang the Chieftain of Brethil feared and dishonoured Húrin, imprisoning and trying to kill him. Húrin's cause was defended by Manthor, and they managed to set the Folk of Brethil against Hardang and slay him. But Manthor himself was killed, and guessed the will of Húrin: "Was not this your true errand, Man of the North: to bring ruin upon us to weigh against thine own?"
Húrin met up again with the outlaws, and together they went to Nargothrond, where Húrin killed the Petty-dwarf Mîm who had claimed the treasure of Glaurung, earning a curse on the gold. Húrin and his outlaws brought the treasure, including the Nauglamír, to Doriath, insulting Thingol by giving it as a fee for his 'good care' of Húrin's kin. Húrin thus brought a curse on Doriath as well, eventually leading to its downfall.
Melian's kind words managed to break through to Húrin's clouded mind, and Húrin finally saw that all his deeds had only aided Morgoth. A broken man, he was rumoured to have cast himself in the sea and killed himself. That was the end of Húrin, who had been known as the "mightiest of the warriors of mortal men".