Middle-earth
Another example is C. S. Lewis's "Space Trilogy," in which Earth is also called Middle-earth. Lewis's novels are situated at the approximate time of World War II, with the last novel, "That Hideous Strength," taking place in post-war England, and they specifically bring in references to Tolkien's legendarium (at that time largely unpublished) and treats these references as primary fact within Lewis's fiction. Merlin, of King Arthur fame, is treated as a successor to the Atlantis magic found within "Numinor" (Lewis's unintentional misspelling of Númenor), and similarities can also be found in the Quenya name for Númenor, which is "Atalantë," and Lewis specifically references the earth as Middle-earth twice, both in Chapter 13, "They Have Pulled Down Deep Heaven on Their Heads". Lewis's borrowings came directly from Tolkien himself: they were close friends and shared each other's literary creations. Lewis encouraged Tolkien to persevere with his Middle-earth writings.A small selection from the many books about Tolkien and his created world:
Reception of J. R. R. Tolkien
Bootleg paperbacks published by Ace Books eventually found their way into colleges in the US in the 1960s. In response, a revised, authorized edition was published by Ballantine Books. The "hippie" following latched onto the book, giving its own spin to the work's interpretation, such as the Dark Lord Sauron representing the United States military draft during the Vietnam War, to the chagrin of the author who stated that "Many American fans enjoy the books in a way which I do not". 
Many fantasy series written in the period were created by fans of "The Lord of the Rings", such as the "Shannara" books by Terry Brooks.
There were active Tolkien enthusiasts within science fiction fandom from the mid-1950s. The first organized Tolkien fan group was "The Fellowship of the Ring", founded by fans including Ted Johnstone and Bruce Pelz at Pittcon, the 18th World Science Fiction Convention (Worldcon) in 1960. Articles on "The Lord of the Rings" had appeared regularly since 1962 in the science fiction fanzine "Niekas", edited by Ed Meskys.