I am wondering if Isildur had destroyed the One Ring by throwing it down into the lava of Mount Doom, would doing this have resulted in the 3rd Age of Middle-earth being dominated by men?
Would the 3rd Age of Middle-earth have been dominated by men if Isildur had destroyed the One Ring in Mount Doom?
3Just because Sauron is dead doesn't mean that the Dominion of Men begins immediately. Even after the Siege of Barad-dûr, the Elven hosts were mighty, and they would not have instantaneously decamped to Valinor. If anything the Third Age would have been even more a transitional age than it was. And not all ages are named "Age of X."– DavidWJul 1, 2022 at 17:48
3This question is not opinion based and I wish people would be less aggressive about closing questions. It’s not opinion based because you don’t know the answer. The Three were in part specially designed to slow and prevent the Fading of the Elves, so their earlier destruction (via the One) would therefore have led to earlier Elven departures.– ShamshielJul 3, 2022 at 14:01
For the time comes of the Dominion of Men, and the Elder Kindred shall fade or depart.
--Gandalf, Book VI, "The Steward and the King"
Your question brings us to one of the most important passages from the books, probably the most important, that Peter Jackson left out of his movies.
It happens after the destruction of the One Ring, as Gandalf, Elrond, Galadriel, and the Hobbits are travelling north through the wilds of Eregion. On the road, they overtake a couple of old beggars who turn out to be Saruman and Wormtongue. Saruman is very bitter at the dashing of all his plans. When Galardiel offers him one last chance to repent, but he takes it as an insult.
'Go!' he said. 'I did not spend long study on these matters for naught. You have doomed yourselves, and you know it. And it will afford me some comfort as I wander to think that you have pulled down your own house when you destroyed mine. And now, what ship will bear you back across so wide a sea?' he mocked. 'It will be a grey ship, and full of ghosts.' He laughed, but his voice was cracked and hideous.
-- Saruman in Book VI, "Many Partings'
Now, of course Saruman is viewing this through his own lens of power-seeking. However, there was a grain of truth in his statement.
The Elven refuges of Imladris and Lothlórien were sustained in part by the power of their bearers' Rings:
'It is long since any of my own folk journeyed hither back to the land whence we wandered long ago,' said Legolas, 'but we hear that Lórien is not yet deserted, for there is a secret power here that holds evil from the land.'
Galadriel had already realized the destruction of the Ring would undo this after refusing the ring when Frodo offered it to her:
'I pass the test. I will diminish, and go into the West, and remain Galadriel.'
Elrond and Galadriel left the realms their power had sustained and sailed to the Undying Lands. Celeborn tried to make a go of East Lórien but he, too, eventually left.
The other bearer of one of the Three Rings knew it, too:
'The Third Age was my age. I was the Enemy of Sauron; and my work is finished. I shall go soon."
--Gandalf, Book VI, "The Steward and the King"
Had the One Ring been destroyed earlier, it's easy to conclude the diminishment of these Elven realms would have happened correspondingly sooner. There would have been no need for the Istari.
So yes, if the destruction of the One Ring at the end of the Third Age ushered in the "Age of Men", then its destruction at the end of the Second Age would have made it happen sooner.
But now it's time for a little frame challenge, because this term "the Age of Men" is really ambiguous. You could say the Age of Men began much earlier than the destruction of the Ring; most of the events of the Third Age, and a preponderance of those in the Second Age, were driven by the deeds of Men rather than Elves. Númenor, Gondor, Arnor, Angmar, the Wainriders, Rohan. And don't forget the Shire.
1The Three seemed to have played a role in preventing the Fading of the Elves, may be worth mentioning. Jul 3, 2022 at 13:48
In the FOTR movie there is a passage quite similar to the first quoted sentence (scene 24 in the extended edition, I don't remember whether it's in the theatrical one too): [ELROND] The time of the elves is over. My people are leaving these shores. Who will you look to when we've gone? The dwarves? They hide in their mountains seaking riches, they care nothing for the troubles of others. [GANDALF] It is in men we must place our hope.– lfuriniJul 3, 2022 at 15:01
2I think it's pretty clear that the Elves were in decline following the First Age. In the middle of the Second Age, Gil-galad needed the help of Númenór to stop Sauron in Eriador, while Ar-Pharazon needed no such help at the end of the Second Age in capturing Sauron. In the Third Age, the remaining Eldar played a supporting role in Arnor's struggle against Angmar (and the Northern Kingdom still fell), while Gondor held out until the end with no comparable aid.– chepnerJul 5, 2022 at 20:45
1@chepner In the case of the Second Age, that probably said more about just how strong Numenor was, rather than a weakening of the Elves. Arnor was also hurt by a mix of its losses in the War of the Last Alliance and the Gladden Fields (which it never truly recovered from), plus later fragmenting into Arthedain/Cardolan/Rhudaur. I also believe there was only one time the Elves helped fight Angmar, prior to the last battle, when they fought alongside Gondor to finish it off, just after Arnor fell. Jul 5, 2022 at 22:25