As I've said before, the popular literature will show the generational themes of the current generation. While I'm sure other literature is submitted, perhaps even published, it will not be popular or remembered as classic.
That in mind, lets look at the Hobbit. The Hobbit is a basic quest novel, published in 1937, but of course written prior to that, it was actually finished in 1932. (Similar to Superman, who was created about that time, but did not see the light of day until much later.) So what is the purpose of this quest? To steal a treasure from a greedy dragon, who has devastated a large number of dwarfs and their town for the sole purpose of enriching himself.
This is so obviously relevant to the stock market crash and the subsequent collapse of soverign debt across Europe and the World that it hardly needs comment. The Hobbit is a reflection of the underlying concerns of the time, whether the author was aware of it or not.
So what about "The Lord of the Rings"? Most of this trilogy was written during WWII, during the depths of the crisis. Also a quest story, the quest in this case requires the mobilization and cooperation of several more or less antagonistic races, dwarfs, elves, men and hobbits. Moreover, not all the individuals share the same goals, some want to use the ring as a weapon against evil, others just want to hide it, and some want to destroy it so it can't be used at all.
Eventually, cooperation wins out and the ring is destroyed, by the action of the least of the characters in the story, Gollum, who destroys it by accident while trying to steal it, an act which actually has no chance at all of success in the larger scheme of things.
And again, Lord of the Rings is obviously relevant to the generational themes of its day.
This has become so plain to me that I'll go so far as to say that virtually any truly popular literature with large scale public approval will have to match the generational cycle. It's nearly impossible to find a clear counter example.