Of the Rings of Power and the Third Age
Of the Rings of Power and the Third Age is the fifth and last part of The Silmarillion by J. R. R. Tolkien. It is relatively short, consisting of about 20 pages. Tolkien's first draft of this was written before June 1948 as he refers to it in a letter then.
The work is a fictional historical essay dealing with the preamble to the events described in Tolkien's epic novel The Lord of the Rings, and the events themselves, in the style of The Silmarillion. As the name implies, the events of the essay are focused around magical artefacts: the Rings of Power, and also the history of the Second and Third Ages of Middle-earth.
After Tolkien's death in 1973, his son Christopher completed this part, assisted by Guy Gavriel Kay. Of the Rings of Power and the Third Age bears some similarities to Elrond's narrative in "The Council of Elrond", a chapter in The Fellowship of the Ring: neither text divulges any details about how Arnor was destroyed or how Gondor became kingless.
Information on the background and development of this essay can be found in The Treason of Isengard.
The Second Age
In the First Age, the cunning and malevolent being Sauron had been the chief servant of the evil fallen Vala Melkor (later called Morgoth) and he was instrumental in Morgoth's many attempts to become ruler of Middle-earth. At the end of the First Age, the Valar (whose power governs the world) unite with Men and Elves to defeat Morgoth, who is captured and cast into the Void. But Sauron (along with other servants of Morgoth, including Balrogs and dragons) manages to escape his master's downfall. Those men who fought on the side of the Valar are allowed to live on the island of Númenor close to Aman where the Valar live, while Middle-earth itself is largely abandoned to Sauron and his minions at the beginning of the Second Age.
The Rings of Power
However, not all of Middle-earth remains under Sauron's sway. Those Elves who had survived the vicissitudes of the First Age begin a new kingdom in Eregion, and during the Second Age, the Elves of Eregion forge many magical rings, including 19 Rings of Power with the aid of Sauron. At this time Sauron is still able to put on a fair appearance and manages to fool the elves into believing his intentions are good. But he deceived them, for in secret he had made the One Ring for himself in order to enslave them and all the other peoples of Middle-earth.
Sauron's plan fails, however: the Elves discover his plot and discard their Rings until they could be shielded from his influence. Sauron then waged war upon the Elves, capturing all the Rings of Power except three which were hidden as he had no part in their creation. While many Elves are killed and the kingdom in Eregion destroyed, the Men of Númenor help the Elves and repel Sauron. After the war, Sauron distributed seven rings to Dwarves and Nine to Men. The dwarves proved immune to his influence, becoming only inflamed with greed for gold, but Men prove weaker. The nine men that had received the rings became great lords, kings, and warriors of their time eventually fell under Sauron's sway, becoming in the end the Nazgûl.
Founding of Arnor and Gondor
Hundreds of years later, the Men of Númenor decide to capture Sauron to demonstrate their might, unaware of the One Ring and the power Sauron wielded when he wore it. As it is described in Akallabêth, Sauron is brought to Númenor as a hostage and appears to show remorse for his deeds. However, he has taken on a beautiful appearance and his seeming goodness and persuasive tongue soon corrupts most Númenóreans and he becomes the chief adviser to the King. Sauron encourages the Númenóreans to cast aside their traditional reverence for Eru Ilúvatar and to take up the worship of Melkor, or Morgoth, Sauron's former master, and make human sacrifices to him. Under Sauron's influence, the Númenóreans finally decide to challenge the Valar by invading Aman. As a punishment for their transgressions, their fleet is annihilated and Númenor itself is destroyed and sunk beneath the waves, but Sauron again escapes and flees to Middle-earth.
Only a few survivors leave Númenor before it is too late, and led by Elendil the Tall and his two sons Isildur and Anárion, they settle in Middle-earth. They create realms governed in the Númenórean way — Elendil rules over Arnor in the North, and Isildur and Anárion rule together in the great country of Gondor in the South. However, Sauron survived the disaster too, and although he has lost his fair appearance, both he and his One Ring return safely to his stronghold of old in the land of Mordor.
Years pass, and Sauron, who had renewed his might, decides to attack the new realms while they were still weak. His onslaught fails, however, and Elendil, his sons, and the Elven kings fight back. For many years the great coalition (The Last Alliance of Elves and Men, as it became known) besiege Mordor. At last the host breaks through into Sauron's fortress of Barad-dûr. Anárion died first before Sauron broke the siege and the mighty king of the Elves, Gil-galad, challenges Sauron to a duel, and is slain in combat. Finally Elendil fights Sauron, and though he is mortally wounded he manages to overcome Sauron before he dies. Isildur, Elendil's son, approaches Sauron's body and cuts off his finger with the One Ring, breaking Sauron's power and causing his spirit to depart from his body. Sauron later returns as the Necromancer in The Hobbit, and returns later to Barad-dûr by the time of the Lord of the Rings.
The Third Age
Elrond pleads with Isildur to destroy the ring in the fire of Mount Doom where it was made, but Isildur takes it for his own and declares that it was his and his folk's, a consolation after the enormous losses of the war. Thus the Third Age of Middle-earth begins, with Isildur's fateful decision to keep the Ring of Power, which sets in motions the events that will lead to the War of the Ring. Isildur himself dies soon after in a sudden ambush by a band of Orcs. Isildur tries to escape by putting on the Ring but it betrays him, falling off his finger, and it is lost in the great river Anduin.
Heirs of royal blood are chosen to lead Arnor and Gondor. For a millennium, both realms enjoy relative freedom and prosperity. However afterwards, Arnor became subject to attacks from the north-eastern kingdom of Angmar, a kingdom that was ruled by the Witch-king, leader of the Nazgûl. More and more people flee from the North, and although Angmar is defeated by the beginning of the third millennium of Third Age, Arnor is no more. Its people are scattered, and its royalty decrease in number and fame; however they remain true to their Númenórean descent. They become the Rangers of the North, protecting the paths of the North from the menace from the East.
Meanwhile, Gondor prospers for much of the Third Age. This begins to change in the beginning of its third millennium, however, when Gondor is assailed by Orcs and Men from the nearby Mordor. For a long time, no one suspects that the same force that had driven the attacks upon Arnor is now fighting Gondor.
Arrival of the Wizards
A thousand years earlier, several Wizards had come to the land: Saruman, Radagast, Gandalf, and the Blue Wizards. Unknown to the peoples of Middle-earth, they are emissaries from the West, sent on behalf of the Valar to help them to obtain their freedom. For many centuries they were silent, and little was done by them apart from observation and counsel. However, as the times darken, they decide to take action against a mysterious dark force which seems to dwell in the middle of a giant forest called Mirkwood. During the attack, the force flees to Mordor and they discover that it was the spirit of Sauron, who was previously thought to have perished. And in the same year, the One Ring is found. Also, in the narrative, it says that Gandalf thought that Sauron was quite capable of bringing all of Middle-earth under his sway even without the One Ring, perhaps explaining at least in part Gandalf's opposition to throwing the One Ring into the Sea at the Council of Elrond.
War of the Ring
Sauron makes war on Middle-earth again, but Frodo Baggins goes to Mount Doom and destroys the Ring, defeating Sauron. (Note that this book specifically credits Frodo with the destruction of the Ring. It does not mention that, in the end, he in fact gave in to the Ring's temptation, and did not give it up willingly, as recounted in The Return of the King.)
After this, it is made clear that Gandalf bore the Red Ring, Narya, and that Galadriel and Elrond had the other two rings. Aragorn son of Arathorn (direct descendant of many of the characters appearing earlier in the printed Silmarillion) is briefly mentioned as returning to claim the kingship and fighting a great field of battle before the City of Gondor.
The essay finishes with the departure of the Keepers of the Rings from the Grey Havens (at the end of The Lord of the Rings) and then the sailing of the Last Ship of the Eldar ever to leave Middle-earth. Thus, "an end had come to the Eldar, of story and of song".