The Necromancer's Campaign

The Necromancer's Campaign was a conflict in TA 2941 when Sauron began to grow in power in the abandoned fortress of Dol Guldur and wished to conquer Erebor for its strategic position to retake the lands of Angmar. The conflict ended with the Battle of Five Armies where Sauron's forces from Dol Guldur were all defeated and having returned to Mordor following the White Council's attack on the fortress, Sauron was unable to continue his campaign.
== Prelude ==
In TA 2940, Sauron secretly reappeared. He allied himself with Smaug and with the chiefs of the Gundabad Orcs of the Misty Mountains, Azog and his son Bolg. Azog payed homage to Sauron and gave him Thror's Ring, the last of the Seven, which he captured from Thráin II at the Battle of Moria a hundred years prior.
Sauron released the Ringwraiths from their entombment in the High Fells of Rhudaur. With Azog as his champion, he wanted to re-establish the realm of Angmar, with which he could attack the Elven realms of Greenwood, Lorien, Rivendell and Lindon, and holds the Dwarves of the Iron Hills at bay. This, he reasoned, would leave the Mannish realms of Gondor and Rohan isolated when he himself returned to Mordor.
To do so, he settled in the ruined, abandoned fortress of Dol Guldur and summoned Moria Orcs and Wargs to its cesspitts. He intended to begin his plan by taking Erebor, expanding Angmar's domain further east and cornering the people of Rhovanion. This would also give him access to the riches of Erebor and allow him to unleash Smaug on the nearby realms. Azog, he reasoned, would be his champion, but the Orc for his part simply wanted vengeance upon Thorin Oakenshield who humiliated him in the Battle of Moria and had since gone to the Blue Mountains. The Necromancer promised him Thorin's head.
== The Conquest ==
Sauron's presence cast a shadow over the world, particularly around Greenwood where Dol Guldur was positioned. The forest grew sick and dark, and the woodsmen who lived there began calling it Mirkwood, and identified Sauron as The Necromancer, a human sorcerer.
Sauron bred Giant Spiders of the spawn of Ungoliant (through Shelob) in the ruins of Dol Guldur, and they were spotted in Rhosgobel in the South of Mirkwood, the home of Radagast the Brown, one of the Five Wizards.
Finding this act suspicious, the Brown wizard goes to investigate Dol Guldur before he is attacked by the resurrected Witch-king. Radagast averted the attack and seized the specter's dagger, the Morgul Blade. Radagast later sees the Necromancer from the shadows, but immediately leaves, barely escaping with his life from the Bats which reside in the fort, and set out to find Gandalf.
Sauron's influence extended beyond the Misty Mountains, where Trolls came down from the Ettenmoors and raided a farm on the outskirts of Staddle. This, along with spies of Azog sent to locate Thorin, aroused the suspicion of Gandalf the Grey Wizard just as Radagast came to warn him and gave him the Morgul Blade as proof. At this point, the Orc Yazneg began hunting Thorin and Company (with whom Gandalf was in train) in the name of Azog, partially out of vengeance and partially because Sauron wanted to stop them from reclaiming Erebor or slaying the dragon.
When the company arrived in Rivendell, Gandalf took his case to the White Council. Saruman and Elrond were skeptical, saying that an isolated Orc attack and Troll infestation are "hardly a prelude to war", but Galadriel believed Gandalf - saying that "something moves in the shadows unseen" and that "every day it grows in strength" - and the reveal of the Morgul Blade started convincing Elrond as well.
Sauron's evil drew the Ring out of its hiding with Gollum under the Misty Mountains. It intentionally fell out of Gollum's pocket in order to be acquired by a Goblin imp who fell into his cavern, but Gollum killed the Goblin. Bilbo, a Hobbit and a member of Thorin's company, was captured by the Goblins and fell with the imp, ends up taking the Ring, which he manages to keep a secret of all but Gollum (whom he evades) and Gandalf.
Sauron tells Azog to stay in Dol Guldur and ready the army, and the Orc sends his son Bolg after the company in his own stead. Beorn helps keep them off of the company's back, telling Gandalf that Orcs infest the Anduin Vales and that Moria Orcs are gathering in Dol Guldur. As the company enter Mirkwood, Gandalf sees the sign of the Red Eye (being Sauron's banner) which compels him to go and investigate the High Fells which he finds open from the inside.
Gandalf sets for Dol Guldur, and asks Radagast to summon Galadriel. He discovered Thrain lost in Dol Guldur, as well as the hidden Orc armies in the cesspits, but is confronted by Azog and finally by Sauron himself. Gandalf is unable to save Thrain, but fends Sauron off before he is revealed in his true form and identity.
Sauron has informed Smaug of the company's approach, but when Bolg tracks the Dwarves to Laketown he sends messengers to inform Sauron that Thorin had already left for Erebor. In turn, Sauron unleashes his army which marches towards the mountain under Azog's leadership.
Sauron kept Gandalf imprisoned, hoping to draw the keepers of the other two Elven Rings to him. He retrieves the Morgul Blade from him, and his Orc Dungeon Keeper nearly harvests the Elven Ring of Fire from the wizard when Galadriel had come to rescue him. However, as she and an unconscious Gandalf leave, they were cornered by the Nazgul, but Elrond and Saruman were not far behind, and aided her as Radagast entered and was able to get Gandalf out.
After the Nine are defeated, Sauron appears himself, but is banished by Galadriel who appears in wrath and uses her phial. Her power is spent (and the High Elves begin their retreat from Middle Earth) but Sauron is banished into the East. Elrond suggests that he will likely return to Mordor, and tells Saruman to warn Gondor to reset their watch on the Dark Land. The Wizard reassures him and tells him to take Galadriel back to her country and leave Sauron to him.
Meanwhile, Sauron's army (reinforced by Bolg's army of Gundabad) arrives at the mountain but is held back by the armies of Dale and the Woodland Realm (which have gathered there to besiege Thorin in Erebor for the sake of earning remunerations from his hoard) and of the Iron Hills (sent to Thorin's aid). Azog risks the course of the battle to draw Thorin out, and is defeated by the dwarf (who is dealt a mortal wound) and Legolas slays Bolg, while the Gundabad Army is defeated by the Great Eagles and Beorn, summoned by Radagast.
== Aftermath ==
In the intervening years, Sauron returned to Mordor and began multiplying Orcs and rebuilding his tower of Barad-dur. Saruman went to Isengard to keep a watch, but using the Palantir he confiscated in Dol Guldur eventually resulted in him being convinced by Sauron's superiority and submitting himself to the Dark Lord.
Gandalf and Legolas joined a young Aragorn who, along with the sons of Elrond, helped cleanse Eriador of evil creatures left over from the Angmar Wars. Aragorn later travelled under pseudonym to Rohan, where he rode to war with Thengel, and to Gondor where he served the steward Ecthelion in the fight against Sauron. The stewards of Gondor kept the forces of Mordor at bay in Ithilien.
Meanwhile, the High Elves began leaving for the Grey Havens. In TA 2994 Orcs retook Moria from Balin, news of which had even arrived at the the Shire within a couple of years.