Mordor was formed by volcanic erruptions from the Orodruin. The first to occupy the Mountains of Mordor was Shelob, who lured all Elves and Men away from her borders, or ate them. Near S.A. 1000, Sauron took over it as his lair. Near Orodruin, he built his fortress, Barad-dûr. After this, he became globally known as the Dark Lord of Mordor. Here he forged the One Ring to Rule them All. Sauron ruled Mordor for two and a half thousand years without interruption, having destroyed and betrayed Eregion and influenced some Easterlings to join him. However, he later journeyed to Numenor, causing its destruction.
Battle of the Last Alliance.Edit
After Gil-galad and Elendil united against Sauron, they finally broke into Mordor through the Black Gate, causing its downfall. Elendil and Gil-galad were both slain, yet Isildur and Anarion remained. Isildur took the One Ring by cutting it off Sauron's finger, causing Sauron to lose physical form. After this, Gondor kept a watchful eye on Mordor at all times.
After the Great Plague, Mordor was no longer kept on lockdown by Gondor, causing it to be filled with evil things. It was during this time when Minas Ithil fell by Nazgul hands. It later became known as Minas Morgul. All other fortifications that were suppose to defend Gondor from the menace of Mordor were used by the orcs to shield Mordor. Sauron, at the meantime, chilled off in Dol Guldur until the White Council came and disturbed his peace. Sauron was forced to leave Dol Guldur and move to Mordor, where he eventually fortified it to the point so no known army, at that time, known to the Free People could destroy it. Gondor, Rohan and Dale are now currently trying to push it down, but might not be enough to destroy this global superpower.