What was the name of Tolkien’s first major Middle-earth book published after The Hobbit?

The Lord of the Rings was Tolkien’s first major Middle-earth book published after The Hobbit.

The Lord of the Rings was published in three volumes between 1954 and 1955. The Fellowship of the Ring appeared in 1954, followed by The Two Towers and The Return of the King. Although it is commonly called a trilogy, Tolkien conceived it as one novel divided into volumes for publication.

The story follows the attempt to destroy the One Ring in Mount Doom. Frodo Baggins carries the Ring from the Shire, while the Fellowship and later groups resist Sauron’s attempt to conquer Middle-earth. The work is much more complex and darker in tone than The Hobbit, reflecting the scale of Tolkien’s invented history.

The Silmarillion was published only after Tolkien’s death, in 1977, and was edited by his son Christopher Tolkien. It presents mythology and history from earlier ages, so it is not the book published immediately after The Hobbit.