John stefan, you effectively asked this question in another thread as well, where
Erestor Arcamen answered you in the second post.
But this
is a decent question, and the answer to it, perhaps, is not straightforward as at first seems.
There is a section of
Morgoth’s Ring, “Myths Transformed”, which addresses this very question. And as we shall see,
Tolkien actually had a vision of how
Melkor Morgoth weakened over time.
In part “VI: Melkor Morgoth”, Tolkien begins (the abbreviation “sc.” is short for
scilicet, itself a Latin abbreviated form of
scire licet, “it is permitted to know”, meaning
that is to say),
Melkor [was]
far more powerful in original nature… The greatest power under
Eru (sc. the greatest created power … [Eru] was to make …
Manwë [was] a little less great…)
… Note that in the early age of
Arda [Melkor] was alone able to drive the
Valar out of
Middle-earth into retreat.
The war against
Utumno was only undertaken by the Valar with reluctance, and without hope of real victory… But Melkor had already progressed some way towards becoming “the Morgoth, a tyrant … + his agents” Only the total contained
the old power of the complete Melkor; so that if “the Morgoth” could be reached or temporarily separated from his agents he was much more nearly controllable… The Valar find that they can deal with his agents (sc.
armies,
Balrogs, etc.) piecemeal. [T]hey … find that “the Morgoth” has no longer … sufficient “force” … to shield himself… Manwë at last faces Melkor again, as he has not done since he entered Arda. Both are amazed: Manwë to perceive the
decrease in Melkor as a
person, Melkor to perceive this also from his own point of view: he has now less personal force than Manwë, and can no longer daunt him with his gaze.
… [Melkor] is “dispersed”. But the lust to have
creatures under him … has become habitual and necessary to Melkor, so that even if the process was reversible (possibly [but only] by absolute and unfeigned self-abasement and repentance...) he cannot bring himself to do it. As with all other characters there must be a
trembling moment when it is in the balance: he nearly repents – and does not, and becomes much wickeder, and more foolish.
Apologies for the long citation, but this is important: By dominating others, setting his will and power into them, Melkor fundamentally weakens himself.
Notice also Tolkien’s reference to “
a trembling moment” when Melkor nearly repents, but fails. This is a
repetitive theme in
The Lord of the Rings. We see it when
Frodo offers
Galadriel the One Ring, but she chooses to “diminish and go into the West and remain Galadriel”; when
Gandalf presents
Saruman with an offer of clemency and freedom, but he chooses to rule over his ruined plans; when Gandalf asks
Denethor to leave the Houses of the Dead and forego suicide, to join his nation and his
city in their defense, but he refuses; when
Sméagol finding Frodo and
Sam asleep outside
Shelob’s Lair nearly repents, but Sam awakes and rebukes him, and selfish hatred seizes final control of
Gollum (Tolkien said this scene grieved him most); when
Faramir confronts
Éowyn about her feelings towards him, and she chooses to claim her
Númenórean heritage, addresses the Valar, and returns his love (my favorite scene in the whole book); and when Frodo offers
Wormtongue an opportunity to part from Saruman
Sharkey, Saruman kicks him in the face, and Wormtongue murders him instead. Add to this the repentance of some of the
Noldor when
Mandos confronts them and speaks his Doom during their northward march along the coast of
Aman to Middle-earth in their folly to attempt the recovery of
Fëanor’s silmarilli from Morgoth in
Silmarillion; and I think there are indications that
Ar-Pharazôn also nearly repented when he at last saw the shore of Aman just before his invasion landing, but instead steeled himself to his deicidal purpose. There is also the situation with
Sauron at the end of the
First Age, when he presents himself to
Eönwë and seems to repent (in fear of the
Host of the West), then chooses not to return to
Valinor and humble himself before the Valar and make what would no doubt have been a long penitential servitude of others.
Now let us move on to the essay “Notes on motives in
the Silmarillion” in “Myths Transformed”. (If you hang around Tolkien boards long enough, you’ll find it’s often referenced and quoted.) It begins,
Sauron was “greater”, effectively, in the
Second Age than Morgoth at the end of the First. … [T]hough he was far smaller by natural stature, he had not yet fallen so low. Eventually he also squandered his power … in the endeavour to gain control of others. But he was not obliged to expend so much of himself. To gain domination over Arda, Morgoth had let most of his being pass into the
physical constituents of the Earth – hence all things … were liable to be “stained”. Morgoth … [eventually had to] wage[] … war almost entirely by means of devices, or of subordinates and dominated creatures.
Sauron, however, inherited the “corruption’” of Arda, and only spent his (much more limited) power on the Rings; for it was the creatures of earth, their minds and wills, that he desired to dominate. In this way Sauron was also wiser than Melkor-Morgoth.
… “Morgoth” … was enraged by the mere fact of the[] existence [of other inhabitants of Arda, with other wills and intelligences], and … [h]is sole ultimate object was their destruction. …
Sauron never reached this stage of nihilistic madness.
If I understand this correctly, I believe that Melkor was the greatest of all the created beings, the greatest of the Valar, but by his continual efforts to control and dominate others, he dispersed his power throughout Arda until he was himself physically and spiritually incapable of the achievements he could make originally, so that Sauron’s power, at the end of the Second Age, when he had dispersed
the Rings of Power and begun to dominate Middle-earth through them, so that he could sacrifice the
Númenóreans on his altar to Morgoth and manipulate them into war against the Valar, was
effectively more powerful than his old master. But Sauron’s body was destroyed in the Downfall of
Númenor, and he was weakened; after he made his second manifestation, he was defeated by
Gil-galad and
Elendil in the Last Alliance, and his
Ruling Ring taken by
Isildur; so that at the end of
the Third Age, though still so powerful that Gandalf feared to confront him even through a
palantír, in his third manifestation he was much weaker than ever before; and then, of course, his power was forever dispersed with the destruction of
the Ring.
In “Notes on motives in the Silmarillion” we also find this observation:
… Morgoth lost … the greater part of his original “angelic” powers, … while gaining a terrible grip upon the physical world. … Sauron’s relatively smaller power was concentrated; Morgoth’s vast power was disseminated. The whole of “Middle-earth” was Morgoth’s Ring…