While Tolkien made the statement that there was no implied allegory in LOTR, I did pick up the following things:
- LOTR can be read as an allegory of WW2.
- LOTR can be read as an allegory of the industrial revolution of the West (Saruman's "mind of metal and wheels", the endless smoke from Mount Doom) and all the evil it entails for rural man (the hobbits).
- LOTR can be read as an allegory of the history of Christendom. It helps if one has read The Silmarillion. The Silmarils being analogues for the light of Christianity.
As for catholic allegories, ones that jumped out at me were:
- Gandalf is an archangel and a keeper of the sacred fire (the word of God being an all-consuming fire).
- The other wizards can also be seen as angels, Saruman being Azazel, one of the fallen.
- Elves are ante-deluvian man with their extremely long life spans and the knowledge such a long life makes possible.
- The most obvious one for me: Aragorn is Jesus whose Kingdom will be established when evil has been conquered forever.
- Sauron is Satan, the corruptor and enslaver. Again, a very obvious one.
It also helps if one has read the Apocryphal Texts. Most notably the two books of Enoch which seems to have served as a strong influence for The Silmarillion.