J. R. R. Tolkien built a process of decline and fall in Middle-earth into both The Silmarillion and The Lord of the Rings.
The pattern is expressed in several ways, including the splintering of the light provided by the Creator, Eru Iluvatar, into progressively smaller parts; the fragmentation of languages and peoples, especially the Elves, who are split into many groups; the successive falls, starting with that of the angelic spirit Melkor, and followed by the destruction of the two Lamps of Middle-earth and then of the Two Trees of Valinor, the destruction of Gondolin, and the cataclysmic fall of Númenor.
The whole of The Lord of the Rings shares the sense of impending destruction of Norse mythology, where even the gods will perish. The Dark Lord Sauron may be defeated, but that will entail the fading and departure of the Elves, leaving the world to Men, to industrialise and to pollute, however much Tolkien regretted the fact.
Scholars have stated that Tolkien was influenced both by the fatalism of Old English poems like Deor and by the narratives of decline in classical Greek and Roman literature, especially Plato's tale of Atlantis which Tolkien explicitly linked to Númenor. Tolkien was influenced, too, by his fellow-Inkling Owen Barfield's theory that all modern languages derived by fragmentation from an ancient language that had a unified set of meanings. From this Tolkien inferred the division of peoples. As a Christian, he also had in mind the biblical fall of man from a world created perfect; this too is mirrored in the history of Middle-earth. The decline is shown in particular in the splintering of the created light through repeated re-creations.