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place in post-war England, and they specifically bring in references to Tolkien's legendarium (at that time largely unpublished) and treats these references as primary fact within Lewis's fiction.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:
J. R. R. Tolkien
On 27 October 1916, as his battalion attacked Regina Trench, Tolkien came down with trench fever, a disease carried by the lice. He was invalided to England on 8 November 1916. Many of his dearest school friends were killed in the war. Among their number were Rob Gilson of the Tea Club and Barrovian Society, who was killed on the first day of the Somme while leading his men in the assault on Beaumont Hamel. Fellow T.C.B.S. member Geoffrey Smith was killed during the same battle when a German artillery shell landed on a first aid post. Tolkien's battalion was almost completely wiped out following his return to England.
Tolkien might well have been killed himself, but he had suffered from health problems and had been removed from combat multiple times.