If you want the “backstory” to all of Tolkien’s legendarium, read the Silmarillion. It is tedious beyond belief but it catalogs all the threads, tales, relationships, and legacies from the Trilogy, along with dozens you’ve never heard of.
And when you’re done with that, read all of the stuff that Christopher Tolkien has compiled that shows the earlier drafts and see how the concept of the world and the history evolved over about 50 years of his father’s writing.
Oh, not that bad. Some parts are as dull as the slow sections of the Old Testament, but even in those passages, there will be a well-turned phrase or a sharp bit of irony to keep you going until the fighting starts again.
The language is intentionally grandiose and mythic, but you get used to it, just as you get used to Dumas or Tolstoy after a hundred pages or so.
Oh wow, thanks.
He created his own languages for the stories as well. Trekkies are still jealous with their attempt making Klingon a language.
Indeed, The Silmarillion has all the back stories and more. Yet I would recommend listening to it in 13 parts on YouTube.
Download them and listen to them as an audiobook. I did and it came alive after I had stopped trying to actually read the book. Tedious beyond belief is an appropriate description.
But listening to it as audiobook is sooo much more enjoyable.
Tedious?
It is the one of the most enjoyable books I have ever read.