Today's Date in the Shire
Rohirrim surround and slay orcs. Merry and Pippin escape. Sam and Frodo continue through the Emyn Muil.
Fun and Games
Walk to Rivendell
Malbeth the Seer
Mordor, Sindarin for 'black land', had been a dreary place and the realm of the Dark Lord Sauron for millenia already when it was eventually conquered and freed in the War of the Ring.
Situated in the southeast of western Middle-Earth, far away from a land like the Shire, but dangerously close to Gondor, Mordor extended for around 500 miles from west to east, and some 300 to 400 miles from north to south. However, the name Mordor was also used metaphorically, standing for Sauron's realm of influence, which was at times much greater.
In the north, the Ered Lithui, the Mountains of Ash, were Mordor's natural border to the plains of the Brown Lands, and in the west and south it was protected by the Ephel Dúath, mountains of Shadow.
Where the two mountain ranges met in Mordor's northwest, the great Black Gate, Morannon, lay, which was the main passage in and out of the land. Behind it lay the vale of Udûn, closed by the narrow Isenmouthe.
The heart of Mordor lay directly behind it, in the northwestern part: the desolate plateau of Gorgoroth. Marked most of all Mordor by the dread of Sauron, Gorgoroth was home only to his armies which were stationed there: where there were living things, even they seemed to reflect the hatred of the land's master- flies and thorny bushes in a barren and dry land. To its west lay the pass of Minas Morgul and Cirith Ungol in the Ephel Dúath, and in the middle of the plateau rose the fiery Orodruin, Mount Doom, where Sauron forged the One Ring. His dark tower itself, Barad-Dûr, was located just east of Mount Doom, on an arm of the Ered Lithui extending southward into Mordor.
In Mordor's south lay the wide inland sea of Núrn, around which extensive fields were tilled by countless slaves of Sauron. From there, the armies of Mordor gathered their provisions.
Mordor first became important for the history of Middle-Earth around the year 1000 of the Second Age, when Sauron retreated from the expanding Númenoreans to Mordor and began the building of Barad-Dûr. Not yet capable of waging open war, he finally forged the One Ring 600 years later, and therewith completed the Dark Tower, binding its foundation to the power of the Ring. When Sauron was defeated in the ensuing war with the forces of Eriador, Mordor proved a reliable retreat for him.
Towards the end of the Second Age, Sauron left Mordor for Númenor, when he feignted to surrender to the host of Ar-Pharazôn. After her downfall, Sauron returned and launched the attack on Gondor from his stronghold of Mordor. But for the first time in almost two and a half millenia, Mordor, and eventually Barad-Dûr itself, were attacked and Sauron was overthrown and reduced to impotence by the armies under the Last Alliance.
With this ended the Second Age, and the time of the Watchful Peace began – all passes into Mordor were closely watched and guarded by Gondor, even though in its refuges, the creatures of Mordor still remained. Among the many fortresses the people of Gondor built for that purpose was the tower of Cirith Ungol with its Silent Watchers.
However, with the calamities of the Kin-strife and the Plague, and thus Osgiliath falling into ruin in 1640 TA, Mordor had to be left unguarded by Gondor. Nevertheless, the biggest threats at that time were the Wainriders, and the Witch-King of Angmar in the north of Middle-Earth.
In 1980, he returned to Mordor and there gathered the remaining Nazgûl, besieging and taking Minas Ithil, and capturing the tower's palantír, which became the stone of Barad-Dûr. While Sauron, slowly regainging strength, hid in Dol Guldur to the north, the Nazgûl remained in what soon became renamed from Minas Ithil to Minas Morgul, the tower of dark sorcery, under their presence.
The lengthening shadow of Mordor caused Gondor to desert the land of Ithilien, at the foot of the Ephel Dúath, in 2901. However, the outpost of Henneth Annûn was maintained still, hidden in the mountainside. 41 years later, Sauron was driven from Dol Guldur by the White Council, and finally returned to Mordor, where he openly declared himself, and began rebuilding and preparing it for his designs.
These came a great step nearer to fruition when sometime later, Gollum, former bearer of Sauron's One Ring, was drawn to Mordor, and captured and questioned there. Mordor's reach began extending to the vales of Anduin and beyond in search of the Ring.
As is recounted in The Lord of the Rings, it was, however, the return of the Ring to Mordor which proved the eventual complete downfall of Sauron. Frodo Baggins and Sam Gamgee were able to fulfill their mission and get to Mount Doom, and the unintentional aid of Gollum resulted in them succeeding in destroying the Ring in the fire of Orodruin.
Just before that, Sauron had issued an unsuccessful assault on Gondor, where the forces of Mordor were defeated on the Pelennor. The victors of that day could have been crushed later in front of the Morannon if it had been for strength in arms alone, but the annihilation of the One Ring caused the downfall of Barad-Dûr and its master, and thus the defeat of their armies.
King Elessar afterwards had the slaves of Mordor freed, and continued to hunt down the orcs and other creatures, while keeping close watch over the Black Land. What he could not restore was the permanent damage and harm done both by Mordor, and to the land itself, the extent of which had Tolkien often use the term 'Mordor' figuratively for all intents and acts of destruction and despoiling.
(References: LR passim, cf. especially I,2; II,2; VI,1-3; app. B; Silm: Akallabêth, Of the Rings of Power…)