It was in between his duties as officer that Tolkien began to lay the narrative foundations of what would become Middle-earth. They were “fairy-stories,” so-called: little vignettes, concerning gnomes and sprites and elf-like creatures, the kinds of stories with which Tolkien had been loosely enamored “since I learned to read.” It wasn’t until he was invalided back to England with trench fever during the Battle of the Somme—where two of Tolkien’s closest friends were killed—that “Tolkien wrote out…the haunting epic of Gondolin, a city of high culture which is destroyed in a hammerblow by a nightmarish army.”
More stories followed shortly after, snippets of a larger world beyond the scope of any fairy-story Tolkien would have encountered in his childhood, but which would eventually become the grand mythos of Middle-earth, itself. That mythos would not be called the The Silmarillion until the book’s publication in 1977, four years after Tolkien’s death, but its disparate pieces were brought to life both in the midst and in the aftermath of the Great War: Morgoth and the fall of Gondolin; Eä and the Undying Lands; Ainulindalë and the War of Wrath.
There is a distinct causality between Tolkien’s experiences in combat and the literature he would write (and re-write, and revise, and re-write again) over the fifty-seven years that ensued. War was a catalyst for Tolkien: it was an unprecedented experience that galvanized him to write stories unlike anything the world had ever seen before. “A real taste for fairy-stories,” Tolkien once explained, “was wakened by philology on the threshold of manhood, and quickened to full life by war.”