“Sauron’s, relatively smaller, power was concentrated; Morgoth’s vast power was disseminated. The whole of ‘Middle-earth’ was Morgoth’s Ring.”
Here is a short excerpt:
Things in Middle-earth changed radically as a result of the War of Wrath. The war lasted about 42 years, beginning in the year 545 of the First Age and ending in the year 587. During that time huge parts of Middle-earth — Beleriand, the far northern lands, the inland sea of Helcar — were ruined or reshaped. In Morgoth’s Ring Christopher Tolkien presents a previously unpublished essay by his father which ponders the motives of the various forces in the Silmarillion.
In the first and second parts of the essay JRRT explains how Melkor diminished himself gradually by incarnating himself (as Morgoth) permanently. He did this so as to control the hroa, 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’, 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.
Click on the link below to read the entire essay.