What Happened
The immediate cause was Sauron's discovery that the One Ring had resurfaced in the Shire and his conviction that it would be brought to Gondor or Rivendell for use against him. In the spring of 3019, he launched his forces from Mordor and from allied strongholds before his enemies could prepare a coordinated defence, striking simultaneously against Gondor, Rohan, Lothlórien, and the northern realms of Dale and Erebor so that no one people could send aid to another. The war therefore unfolded on several fronts at once: Théoden's Rohan was assailed by Saruman's army from Isengard even as Minas Tirith faced the main thrust of Mordor's host under the Witch-king, while Elves and Dwarves in the north fought off separate attacks by Sauron's Easterling allies.
The decisive engagements came in quick succession: the destruction of Isengard's army at Helm's Deep, the siege and relief of Minas Tirith culminating in the Battle of the Pelennor Fields, and finally the deliberate diversion of the remaining Free Peoples' strength to the Black Gate of Mordor, a battle fought chiefly to hold Sauron's attention and draw his gaze away from his own borders. Throughout these open campaigns, the true purpose of the war was carried by a small group travelling unseen through hostile country toward Mount Doom, where the Ring alone could be unmade. The armies at the Black Gate fought without expectation of victory by arms, aware that the outcome depended on events unfolding far from any battlefield.
The war ended abruptly with the Ring's destruction in the fires of Orodruin, which brought the immediate collapse of Sauron's power, the ruin of Barad-dûr, and the rout or surrender of his armies on every front. Gondor and its allies moved swiftly to secure the peace that followed, restoring rightful rule in Minas Tirith and clearing the remnants of Sauron's forces from the lands they had occupied. The conflict marked the effective end of the Third Age, closing an era dominated by the struggle against Sauron and opening the way to the Fourth Age and the diminishing of the Elves' presence in Middle-earth.
Course of the War
The war's opening moves preceded its open battles by months. Through the summer of 3018 the Nazgûl crossed the Anduin in secret and searched for the Shire, forcing Frodo Baggins to leave Bag End with the Ring in September; his company reached Rivendell in October after being pursued as far as the Ford of Bruinen. The Council of Elrond, convened soon afterward, resolved that the Ring should be carried into Mordor and destroyed rather than wielded, and the Fellowship of the Ring departed Rivendell on 25 December 3018, opening a covert second front that ran parallel to the mustering of armies elsewhere.
Early in the new year the Fellowship's passage through Moria cost Gandalf his fall in battle with the Balrog, and after a respite in Lothlórien the company was broken at Amon Hen on 26 February 3019. Boromir died defending Merry and Pippin, who were captured by a raiding party of Saruman's Uruk-hai, while Frodo and Sam turned east alone toward Mordor and Aragorn, Legolas, and Gimli set out in pursuit of the captives. The quest thus split into several separate threads that would not converge again until the war's very end.
On the Rohan front Saruman struck first at the Fords of Isen in late February, where Théoden's son Théodred was killed. Gandalf, returned and altered after his fall in Moria, reached Edoras soon after and freed Théoden from the counsel of Gríma Wormtongue, persuading him to ride out against Isengard's forces rather than shelter behind Edoras's defences. The army of Isengard was broken in a night-long assault on the fortress of the Hornburg at Helm's Deep in early March, and the Ents' subsequent attack on Isengard itself flooded the stronghold and ended Saruman's power to make further war.
While Rohan's muster rode east to Gondor's aid, Aragorn led a smaller company through the Paths of the Dead, gathering the oathbreaking dead of the mountains and driving off the Corsairs of Umbar at Pelargir on the lower Anduin. His arrival before Minas Tirith with commandeered ships during the Battle of the Pelennor Fields, in place of the reinforcements Sauron's captains had expected from the south, proved decisive in the battle's final hours and broke the assault on the city.
In the days following the Pelennor, the captains of the West debated their course at Minas Tirith and chose to march what strength remained to the Black Gate, less in hope of victory than to hold Sauron's attention away from the two hobbits still making their way toward Orodruin. The Ring was destroyed on 25 March 3019, and with it Barad-dûr and Sauron's armies collapsed within hours, ending the war's open campaigns almost as suddenly as they had begun.
The war's last action came only months later and far from any battlefield in Gondor or Rohan. Returning home in the autumn, the four hobbits found the Shire under the petty tyranny of ruffians serving a figure known locally as Sharkey, whom they discovered to be Saruman himself, fled north after Isengard's fall. Their rousing of the Shire-folk culminated in the Battle of Bywater in November 3019, the last fight of the war and the only one waged on Shire soil, after which the hobbits set about restoring their own land.
Sides and Leaders
Sauron directed the war from Barad-dûr through the Witch-king of Angmar, Lord of the Nazgûl, who commanded the siege of Minas Tirith in his stead; Mordor's strength was reinforced by Easterling and Haradrim contingents and by the Corsairs of Umbar, whose fleet was expected to reach the Pelennor from the south. Ranged against them stood Gondor under the Ruling Steward Denethor II, Rohan under King Théoden and his marshal Éomer, and smaller forces from Lothlórien, Rivendell, Erebor, Dale, and the Dúnedain Rangers of the North, none acting under a single unified command but converging on the same defence.
Saruman of Isengard occupied an ambiguous position. As head of the White Council he had long been reckoned among Sauron's chief opponents, but Gandalf's account to the Council of Elrond revealed that he had come to covet the Ring for his own ends and had turned traitor to that purpose well before open war began. His assault on Rohan through the army raised at Isengard was waged independently of Mordor, without coordination between the two powers; the sources present him as a rival claimant to dominion whose war served Sauron's aims by opening a second front, rather than as a subordinate ally acting under Sauron's direction.
Aragorn's assumption of leadership drew in allies whose service had lapsed for generations. The Dead Men of Dunharrow, Men of the mountains who had broken an oath of allegiance sworn to Isildur in the Second Age, were summoned through the Paths of the Dead and discharged their debt by helping to rout the Corsairs of Umbar at Pelargir before being released from their long bondage. Their brief return to Isildur's line, alongside the Grey Company of Rangers and Prince Imrahil of Dol Amroth's levies from Belfalas, extended Gondor's command structure beyond the Stewardship in the war's final campaigns.
Consequences
The most enduring political outcome was the restoration of kingship in the south. Aragorn's crowning as King Elessar reunited Gondor and Arnor under a single ruler for the first time since the two realms had drifted apart in earlier ages, ending the long stewardship that had governed Gondor alone and re-establishing a single line of authority stretching, at least in principle, from the Shire's borders to the mouths of Anduin. Gondor's own boundaries were pushed outward again as lands lost or abandoned during the centuries of Mordor's growing shadow were reclaimed or resettled, and the Stewards' house, though its direct rule ended, retained a recognised place beside the restored crown.
Alliances forged in the war's course were formalised once the fighting ended. The bond between Rohan and Gondor, tested and renewed on the Pelennor, was confirmed as a lasting compact between the two realms rather than a wartime expedient, leaving Rohan a free and honoured ally rather than a subject territory. Isengard, emptied of Saruman's power, passed from ruin into the keeping of the Ents, who were left to tend it as a green and guarded place rather than a fortress to be resettled by Men. Further east and south, the peoples who had fought as Sauron's subjects or tributaries were left without the master who had bound them, and the threat they had posed along Gondor's borders receded, though it did not vanish entirely.
The Shire itself emerged from the war with an altered standing. Its hobbits, who had gone to war as an afterthought in the reckoning of the great powers, returned to a homeland formally enlarged by royal grant: the Westmarch, the country beyond the Far Downs, was added to the Shire by the King's own gift, and the Shire's independence from outside rule was thereafter guaranteed rather than merely tolerated. The hobbits' standing among the free peoples changed correspondingly, from a folk barely known outside their own borders to one whose part in events was acknowledged at the highest levels of the restored realm.
More broadly, the war closed the account of the Third Age as an age contested between Elves, Men, Dwarves, and Sauron's will, and opened what came to be reckoned the age of Men's dominion. In the years that followed, the high Elven refuges that had endured through the war began to empty as their people took ship for the West, so that Middle-earth's affairs passed increasingly into the hands of Men, with Dwarves and the remaining free peoples continuing under their protection rather than as independent powers of the first rank. The Red Book tradition that preserved the war's history itself belongs to this transition, a record kept by a diminishing people for an age no longer primarily their own.
In the Narrative
The book presents the war not as an event witnessed from above but as history assembled after the fact, drawn from an account the hobbits themselves are said to have written and kept at Bag End and in Westmarch. This framing keeps the narrative tied to what its participants could see and learn, rather than offering a commander's overview of the whole campaign; readers follow the fighting through the eyes of those swept into it; Pippin at Minas Tirith, Merry riding with the Rohirrim, rather than through any single vantage that could survey both the battles and the Ring's road to Orodruin at once.
That divided viewpoint is built into the book's structure. The chapters that follow the war of arms and the chapters that follow the Ring-bearers are told separately and out of strict chronological step, so that the reader, like the defenders at Minas Tirith or the host before the Black Gate, does not know from within the story how the errand into Mordor is faring while the great battles are being fought. The suspense of the war's later campaigns therefore depends on a withheld piece of information that the characters waging it largely do not have: that their fighting is meant only to buy time, not to win by arms what only the Ring's destruction can settle.
Within the story's own terms, the war of banners and battle lines is made to seem the lesser of its two conflicts. Tolkien's later comments on the book describe its climax as turning not on martial victory but on an act of pity extended long before, when Frodo's mercy toward Gollum preserved the very creature who would inadvertently complete the quest after Frodo himself failed to relinquish the Ring at the Cracks of Doom. Read this way, the armies of Gondor and Rohan perform the visible, heroic half of the tale, while its actual resolution turns on an unheroic failure redeemed by chance and former kindness, a deliberate inversion of the war narrative the earlier chapters seem to promise.
Drafts and Variants
The shape of the war emerged only gradually across Tolkien's manuscripts. At several points in the writing he paused to sketch the unwritten campaigns ahead of him in outline form, sequences Christopher Tolkien titled by the point in the story at which they were drafted, such as "The Story Foreseen from Lórien." These forward sketches already assumed an alliance of Rohan and Gondor against Isengard and Mordor, but left the coordination and outcome of the several fronts unsettled. One notable change concerned Théoden: an early plan had the king killed in the fighting at Helm's Deep itself, which would have removed him from the war before Gondor's relief; Tolkien instead carried him through to a later death on the Pelennor Fields, extending Rohan's part in the war and giving weight to the ride recounted in the corresponding chapters of drafting. Faramir's role in the Gondor campaign was likewise not planned in advance: Christopher Tolkien's commentary notes that Denethor's second son, and his interception of Frodo and Sam in Ithilien, took shape only as the relevant chapters were actually being written.
The hobbits' return to a changed Shire, later fixed as the Scouring of the Shire, was likewise not part of the war's earliest design. Draft material for the closing book shows Tolkien still undecided how much narrative space, if any, the homecoming should receive, and the eventual revelation that the ruffians' leader Sharkey was Saruman himself was arrived at only in the course of drafting Book Six, rather than having been foreseen from the war's outset.