The Nandor (sg. Nando), later known as the Silvan Elves or "Wood-elves", were one of the Telerin races of Elves. The Nandor were the original elven inhabitants of Middle-earth east of Beleriand, but eventually they also stretched out across the Ered Luin as well into Ossiriand. They were the "green elves", loving forests, and easily the most common kindred of elf by the Third Age in Middle-earth.
Lenwë and Denethor
The Nandor were originally simply an group of the Teleri indistinct from the others who were afraid to cross the Hithaeglir, and content to remain in the wide forested lands to the east, along the river Anduin. One of the Teleri, of the silver-haired kindred of Olwë that would later become the Falmari, rose to lead them. He was named Lenwë, and led a great number of the Teleri south along the Great River, where they fell out of the histories for a long time. They called themselves the Nandor, and they loved water and green things. Under Lenwë they developed great knowledge and skill with herbs and living things, tree and beast alike. Their culture became very distinct.1
Gradually, the Nandor spread out. They may have moved on to live in Eriador, or by the mouth of the Sea at the outpouring of Anduin. They were a simple folk, with no weapons of steel. They made friends, too, with the Naugrim, and were contented. But evil beasts came from the north, and they had no defense against such terrible weapons. They had been told by the Naugrim about King Thingol and the might of the Sindar, therefore Denethor, Lenwë's son, crossed over the Ered Luin into Beleriand, the western lands of Middle-earth. There they settled in the green and many-rivered Ossiriand, welcomed by Thingol as long-lost relatives. They were called the Laegrim.2
Wars of Beleriand
Thingol took advantage of their friendship on the first opportunity, when he was in great need. The Dark Lord Belegurth invaded Beleriand, cutting Thingol off from his other strong allies, the Falathrim. But Ossiriand was wide and Morgoth could not sever that connection. Thingol called Denethor to his aid, and the Laegrim came. Thingol attacked the orc-host from the west, and the Laegrim from the east, creating a hammer-and-anvil technique that succeeded. But this victory came at great cost. The Laegrim were lightly-armed, and the orcs shod in iron. Denethor was cut off at Amon Ereb; he and all those nearest about him were killed before Thingol could rescue him. The Laegrim loved him and mourned his loss, and henceforth would take no king. They became reclusive, pulling away from the many troubles of Beleriand, and fighting no longer against Belegurth.2
When the Noldor returned from over the Sea, they gave the Laegrim the name (in Quenya) Laiquendi. The Laiquendi did not participate in the great events of Belegaer throughout the First Age. The Laiquendi accepted Beren and Lúthien, who came to Tol Galen in the midst of their lands, and made it one of the most beautiful places in Beleriand. After the dreadful sack of Doriath and death of Thingol, many of the Laiquendi joined Beren in the Battle of Sarn Athrad. The green elves later sent the news to King Dior Eluchíl news of the final deaths of Beren and Lúthien.3
After the War of Wrath, Ossiriand survived no longer, and the survivors of the Laiquendi once more merged back into the main Nandorin population, who now were spread over the face of Middle-earth. The Nandor on both sides of the mountain range were of a somewhat less pure strain, those in Ossiriand having mixed blood with some Sindar, and those in the east having mixed blood with the Avari who came westwards. As the Second Age went on, the blood became even more mixed. Even their language changed from Nandorin to Sindarin. Gradually, the Nandor were changing into what became known as Silvan Elves or Tawarwaith, meaning "Forest People"5.
The Nandor, now known in their impure state as Tawarwaith, were soon pushed into refuge when Sauron rose to challenge elven power in Middle-earth. Some were forced to take refuge with the Noldor, who although weakened were still very powerful, in Lindon and Imladris. Others dwelt with Círdan the Sinda in Mithlond, and still others hid in their ancient forest homes Lórinand and Eryn Galen. They took leaders from the pure-blood clans of Noldor and Sindar; in the case of the latter two refuges, the Sindarin lords Amdír and Oropher respectively.
The Tawarwaith of Lórinand (the Galadhrim) and Eryn Galen played mostly a small role in the events of the Second Age, as the had in the First. Amdír and Oropher built up their kingdoms as the shadow of Sauron grew longer and longer, and evil more powerful. Both Amdír and Oropher took great hosts to join the Last Alliance of Elves and Men, and fought in the war that followed. Both hosts suffered immense losses; Amdír was cut off and killed in the Battle of Dagorlad with many of his followers, while Oropher rashly disobeyed King Gil-galad in Mordor and fell beside two thirds of the entire company5. The Tawarwaith entered the Third Age greatly weakened and disheartened, despite the seemingly final defeat of Sauron.
Lórinand, now known as Lothlórien, and Eryn Galen, now known as Mirkwood, continued to host the larger populations of Tawarwaith. Amroth took over in Lothlórien, later passing the rulership on to Galadriel and Celeborn, while Thranduil became king in Mirkwood. Under these rulers the Tawarwaith prospered and became numerous once more, while the Noldor and Sindar were in slow but steady decline. Yet though mostly inactive, they were watchful of the growing of men and the ominous change the Third Age would bring5.
But the elves of both Lothlórien and Mirkwood were threatened by a new evil growing in south Mirkwood. The Necromancer was building Dol Guldur. As the Third Age continued and Sauron rose, the White Council was formed. Sauron was driven from Dol Guldur several times, but the Tawarwaith were still for the most part impassive. Eventually the War of the Ring came. Legolas, Thranduil’s son, became a hero of that war, while both Lothlórien and Mirkwood were invaded by Dol Guldur in the Rhovanion Campaign. All attacks were repulsed, and Dol Guldur was thrown down at last in a grand counterattack by Celeborn and his followers6. Mirkwood was renamed Eryn Lasgalen. Yet the Silvan population was again diminished. Galadriel and Celeborn passed west, and the light of Lórien faded.
Throughout the Fourth Age they aided the rising Reunited Kingdom, making Ithilien green, for instance7. Their eventual fate was to pass west to the land they had never seen, or else to remain in Middle-earth Changed and fade into forgetfulness.