Does Sauron wane?

Question

Apparently Tolkien's Middle-Earth is in continuous decline - the greatness of the past is always ebbing away.

Given that, is Sauron also waning? Could he for example conquer Middle Earth, then wane to the point where an uprising overthrows him?

Answer 1

We have it from Gandalf that, had Sauron conquered in the Third Age, none could foresee it ending until the end of time, including Gandalf the White.

Concerning this thing, my lords, you now all know enough for the understanding of our plight, and of Sauron's. If he regains it, your valour is vain, and his victory will be swift and complete: so complete that none can foresee the end of it while this world lasts. (The Lord of the Rings, The Last Battle

Moreover, it's not quite right to say that Middle Earth is in some metaphysical constant decline (well, maybe morally) - that isn't so. Many things were architected so that in some respects, it would appear to us so; for example, the Valar, by design, play a lesser role as time goes on, and so do the Elves, ceding the world to Men. Similarly, some works of magic are so great they can only be done once, but this not in turn require the world to be in continual decline. The Trees could only be made once, Feanor could make the Silmarils only once, Morgoth could only make the world his Ring once, and Sauron could make the Ring only once - and this is because they put so much of themselves into the work.

But consider that Feanor himself, who made the greatest works of the Eldar, was not himself of the first Elves! What he did was greater than all the Elves who came before him. (Indeed, according to Tolkien, many of the first Elves become Avari, who seemingly never did much at all.)

But perhaps a better example, and more pertinent, would be Morgoth. Morgoth himself became personally weaker, yes. But that's because he poured all his power and will into dominating Middle Earth.

Melkor 'incarnated' himself (as Morgoth) permanently. He did this so as to control the hroa,2 the 'flesh' or physical matter, of Arda. He attempted to identify himself with it. A vaster, and more perilous, procedure, though of similar sort to the operations of Sauron with the Rings. Thus, outside the Blessed Realm, all 'matter' was likely to have a 'Melkor ingredient',3 and those who had bodies, nourished by the hroa of Arda, had as it were a tendency, small or great, towards Melkor: they were none of them wholly free of him in their incarnate form, and their bodies had an effect upon their spirits.

But in this way Morgoth lost (or exchanged, or transmuted) the greater part of his original 'angelic' powers, of mind and spirit, while gaining a terrible grip upon the physical world. For this reason he had to be fought, mainly by physical force, and enormous material ruin was a probable consequence of any direct combat with him, victorious or otherwise. This is the chief explanation of the constant reluctance of the Valar to come into open battle against Morgoth. Manwe's task and problem was much more difficult than Gandalf's. Sauron's, relatively smaller, power was concentrated; Morgoth's vast power was disseminated. The whole of 'Middle-earth' was Morgoth's Ring, though temporarily his attention was mainly upon the North-west. (HoME, Morgoth's Ring)

Morgoth only looks personally weaker because all his power and will is disseminated throughout the whole world, corrupting and warping everything material until the very end of time. Given Morgoth's magical influence on the world, even after his execution and ejection, endures until the end, there's no reason to believe that Sauron, with the Ring, his own externalization of power, would also weaken more than he already did: nearly all of his power was already in the Ring, which is why destroying it killed him. (And why being killed while in physical form always diminishes him: he's "spending" himself in a way that's then destroyed.) As Gandalf continues:

For he will lose the best part of the strength that was native to him in his beginning, and all that was made or begun with that power will crumble, and he will be maimed for ever, becoming a mere spirit of malice that gnaws itself in the shadows, but cannot again grow or take shape. And so a great evil of this world will be removed. (The Lord of the Rings, The Last Debate)

As a further note, Tolkien adds that the morgoth-element in matter, is in fact the source of most evil magic, and it will never "go away" without the destruction of all matter:

No such eradication of Morgoth was possible, since this required the complete disintegration of the 'matter' of Arda. Sauron's power was not (for example) in gold as such, but in a particular form or shape made of a particular portion of total gold. Morgoth's power was disseminated throughout Gold, if nowhere absolute (for he did not create Gold) it was nowhere absent. (It was this Morgoth-element in matter, indeed, which was a prerequisite for such 'magic' and other evils as Sauron practised with it and upon it.) (HoME, Morgoth's Ring)

So as long as there is a material world, Sauron can practice magic. And his own power has already been externalized into a (he thought) invincible tool of domination, he doesn't really have much to worry about personally.

Answer 2

He certainly does.

He starts as the greatest servant of Aulë, "god" of invention. Joins Morgoth, loses, and hides in shame. Binds most of his power to The One Ring. Becomes form-locked to an evil warlord after the drowning of Númenor. Loses the Ring and his body again after The Last Alliance. And finally is reduced to a powerless whisper when the Ring is destroyed.

If he had won at any point, he would likely have put more and more of himself into dominating the world and defending against possible Valar invasions over time, gradually weakening until he was basically an empty husk for the Ring to use, much like the ringwraiths.