In 1945, Tolkien moved to Merton College, Oxford, becoming the Merton Professor of English Language and Literature, in which post he remained until his retirement in 1959. He served as an external examiner for University College, Dublin, for many years. In 1954 Tolkien received an honorary degree from the National University of Ireland (of which U.C.D. was a constituent college). Tolkien completed The Lord of the Rings in 1948, close to a decade after the first sketches.
Tolkien criticized Allied use of total-war tactics against civilians of Nazi Germany and Imperial Japan. In a 1945 letter to his son Christopher, he wrote that it was unacceptable to gloat over a criminal's or Germany's punishment, and that Germany's destruction, deserved or not, was an "appalling world-catastrophe". He was horrified by the 1945 atomic bombings of Hiroshima and Nagasaki, referring to the scientists of the Manhattan Project as "these lunatic physicists" and "Babel-builders".
Parallel to Tolkien's professional work as a philologist, and sometimes overshadowing this work, to the effect that his academic output remained rather thin, was his affection for constructing languages. The most developed of these are Quenya and Sindarin, the etymological connection between which formed the core of much of Tolkien's legendarium. Language and grammar for Tolkien was a matter of aesthetics and euphony, and Quenya in particular was designed from "phonaesthetic" considerations; it was intended as an "Elven-latin", and was phonologically based on Latin, with ingredients from Finnish, Welsh, English, and Greek. A notable addition came in late 1945 with Adûnaic or Númenórean, a language of a "faintly Semitic flavour", connected with Tolkien's Atlantis legend, which by The Notion Club Papers ties directly into his ideas about the inability of language to be inherited, and via the "Second Age" and the story of Eärendil was grounded in the legendarium, thereby providing a link of Tolkien's 20th-century "real primary world" with the legendary past of his Middle-earth.