I have always wondered about why the elves left Middle Earth. It seemed to me that they were just running away from the conflict. They mention, in the movies, something about the coming age of humans, but if I lived in Rivendell, I wouldn't be going anywhere regardless of whose age it was.
I have not read any of the books and was wondering if they contain any more explanation on this subject...
Elves are bound by the wheel of fate, so their long lifes are basically an expression of something like predeterminism, like the Istari:Maiar(wizards:Gandalf:Sauron:Saruman:Radaghast and the green and blue wizards who were lords over the sea and the East) Gandalf is the Guardian of Arnor, and since all that remains of Arnor is the Shire after the Witchking of Angmar(Bad dude who stabs Frodo,never been killed by a mortal blade, knows alot of magic himself etc, military genius) Destroyed the old kingdoms of Arnor leaving only the rangers(one of the nine Nazgul and their leader) The line of Isildur, who Aragorn is a direct descendant of.
The elves are there on Middle Earth to perform certain tasks, and to guide mortals, of course the Elves kind of have the ability to change their fate but are still ever tied to it, but when the Elves have achieved what they were sent to do they feel the call of the Undying Lands(where the Valar live(kind of like angels to Eru: god, melkior one of the Valar is Saurons master) Who sent them their in the first place after the wars of the first age) So especially the High Elves who saw the light of the Valar are drawn back by the fate of the Valar. Less so the Grey Elves and less so the Sylvan elves who never saw the undying lands(Legolas).
Half elves have a choice they can either become mortal, not tied to fate or like Elrond bound to fate, and of course his daughter he pleads with has chosen a mortal life, she choses to have the free will of the mortals unbound, I chose a mortal life, as it says in the film. Elrond can't understand it he has chosen immortality and to be tied by fate, but his daughter Arwen has slipped free of the bonds of fate, he pleads, he feels the pull of the west because his fate is decided and now the Elves have done their duty they are tied to their roots.
In the end the Elves receed into the west even the Sylvan elves recieve the call, it seems heartless, but then look at the Elves joining the force at Helms deep, they still feel that they have a duty, what is so heartbreaking is that all these Elves at Helms deep could receed into the west but they honour there duty, they die for something that was set down thousands of years ago.
In the end the Elves are not part of the Earth any more, and so they must go West, and all that is left is the Elven blood in those such as the Dunedain(Aragorn) Why is Aragorn so wise and so good, because he's nearly a hundred, and is blessed with Elven blood, same with the Black Numenorians, but it would take too long to explain the whole of the second age.
You can find alot of this out from the Unfinished Tales, and from Tolkeins myriad of texts that never appeared in the book, suffice to say it's a real mythology he wanted to give to the world: it's a mythology that is so complete and has so many complete languages and histories, that only by looking outside of the books will you find it.
Sorry badly explained remembering of the top of my head.