There is the Kalevala, eddaic literature, Beowulf, Sir Gawain and the Green Knight, the Old and New Testaments (he knew some Greek and Hebrew), Thomas Aquinas and so much more all buried in there, as well as his own syntheses of these many influences in his own thought in ideas like mythopoetics, eucatastrophe, and what is the best thought on fantasy and "fairy stories" to date.
One of the assumptions that suffuses Middle-Earth is that history is the story of a long decline. It was a common assumption of medieval times that the greatness of the past could never be replicated in the present and that the "march of history" is in fact a story of slow, inexorable decay.
Our technological achievements might lure us into dismissing this out of hand, but I am not fully convinced that the corollary is true - that history is a story of steady progress.
Hand in hand with all of our achievements is our growing capacity for abject destruction. Now, I won't get into this argument because it has been said before. We've been shocked aware by two world wars and the threat of nuclear holocaust (weapons only the US has been willing to use, sadly and interestingly) and since the "march of progress" argument has rung a little hollow now and then. For every civil rights victory in the US there is an expansion of child sex slavery or repressive religious regimes or, frankly, a US-sponsored right-wing overthrow of an elected government.
What we don't seem to develop is the moral sensitivity to use our technology wisely. And never before has one nation been able to kill everyone, everywhere, many times over. Is that progress toward anything but absolute ruin? If so, I don't see it.
Perhaps we are heading toward some kind of turn, some realization that has been slowly and secretly building over time. Perhaps we have already set in motion mechanisms which will inevitably destroy us.
Either way, as I have been doing research and listening to lectures on Tolkien's work, and encounter this Medieval paradigm of decay over time again and again, I can't say I have a strong rebuttal ready. We have medicine and technology and information but most of the people on planet Earth don't have access to them anyway. A third of them don't have enough food or clean water. And I'm not clear that we haven't, in aggregate, created more problems than we can solve.