LOTR question?

Question

When did Sauron move into Mordor and set up his base of operations? What prompted him to move there?

Answer 1

The first record of Sauron's presence in Mordor occured during the second age when he attempted to earn the elves' trust under the facade of Annatar, "the Lord of Gifts". He gave them gifts of magic rings of power which he used Mount Doom to forge while secretly creating the one ring to gain dominance over the elves' rings. When the elves learned of his intent, they discarded their rings and the War of the Elves and Sauron began. After many militant strikes, Sauron's army was driven back to Mordor by the elves. At this point, Sauron built Bara Dur as his military base as well as the Black Gate to protect his encampments. At this time, he also forged sixteen rings and distributed them to dwarves and men, the latter becoming the Nazgul. After corrupting the Númenórean kingdom near the end of the second age his body as well as the rest of the kingdom were destroyed by Eru (God) in a great flood. Sauron's spirit returned to Mordor by way of the ring's power and he eventually regained the physical form seen in LOTR: Fellowship of the ring. At this time, he was destroyed by Isildur in the battle by the Alliance and the rest is history.

Answer 2

About the year 1000 in the Second Age. To quote the Master:

"c. 1000: Sauron, alarmed by the growing power of the Nùmenoreans, chooses Mordor as a land to make into a stronghold. He begins the building of Barad-dûr."

Answer 3

I think it was after the ring was lost the first time, and it was the loss of the ring that prompted him - he needed to find it again.