Originally posted by Tar-Palantir
Those Elves that left Aman did so because of Melkor. He attemped to split them from the Valar. After the destruction of the Trees and the theft of the Silmarils (some of?) the Teleri rebelled and left for Middle Earth where they battled Melkor for the Silmarils.
Actually, it was the Noldor that rebelled. Melkor had been captured by the Valar and put in unbreakable chains and kept prisoner in Aman for a long time. Then Feanor (the greatest craftsman of the Noldor Elves) created three great jewels called the Simarils. What made the Simarils so special is that Feanor somehow managed to capture the Light of the Two Trees and imbued the Simarils with them. No one, not even the Valar, could figure out how Feanor did this.
When Melkor was finally freed from his imprisonment for repenting his bad behavior, he secretly plotted to steal the Simarils and destroy the Two Trees. Manwe (the leader of the Valar) believed that Melkor had truly repented, but Melkor tricked him. Once Melkor killed Finwe (the king of the Noldor and Feanor's father), he destroyed the Two Trees and stole the Simarils. Feanor, having lost his father and his greatest work of craftsmanship, whipped his people into a fighting frenzy to make war on Melkor, who had already fled to Middle Earth by this time. To get to Middle Earth, Feanot and his fellow Noldor needed the Teleri's ships to sail across the Western Sea to get back to Middle Earth. Feanor demanded that the Teleri hand over their ships to the Noldor. The Teleri, offended that the Noldor would be so arrogant to demand their ships without being compensated for them, refused. The Noldor then killed many of the Teleri and stole their ships. This was known as the Great Kinslaying, for it was the first time in history that Elf had killed Elf.
It was not to be the last.
Originally posted by Tar-Palantir
After Melkor was overthrown, the Elves were allowed to return to Aman. Some were banned or too proud to return and stayed in Middle Earth. I can't remember if Galadriel was banned or unwilling to return, but because of her actions against Sauron she was allowed return (or decided to) to Aman.
If I recall correctly, Galadriel refused to return to Aman because she had no desire to see her Noldor kin again because she was still ashamed of the Kinslaying. I think her mother was Teleri, but her father was Noldor.
Originally posted by Tar-Palantir
As for Sauron, he has a small part in the 'Two Towers' where Pipin looks into the Palantir.
I can't remember if this has been cleared up but: The Istari are of the Maiar, as was Sauron and the Balrogs. See 'Unfinished Tales'. They are also described as 'peers of Sauron'.
Apologies for the seemingly disprite points here.
Sauron and the Istari were all Maiar, but there is a reason the Istari were notably weaker than Sauron. The Istari were sent by the Valar to Middle Earth with a BIG stipulation: the Istari were forbidden to use any power greater than that which was already present in Middle earth. The Istari were also forbidden to reveal themselves as Maiar. It was their highest priority for the Istari to keep themselves disguised as men of great magic, rather than reveal themselves to the inhabitants of Middle earth as demi-gods. Basically, the Istari had to help Middle earth fight Sauron with one hand tied behind their backs.
Also, Sauron's spirit survived, but he couldn't reform his physical body without the One Ring. The Ring was the "last piece of the puzzle", so to speak, that Sauron needed to take control of Middle Earth again.
