How much of the Middle Earth universe had Tolkien invented when he wrote The Hobbit?

Question

This question was inspired by a comment from Darth Satan.

The Hobbit is a very different sort of work from Lord of the Rings: written in a style more like a children's book and less like an epic saga. I've always thought that Tolkien didn't have many details of the Middle-Earth universe clear in his mind when he wrote it, and that he spent many years inventing it all in the course of writing LotR, but Darth Satan has made a well-referenced assertion that this is not the case.

Some quick Wikipedia research threw up the following:

As Tolkien's work on LotR progressed, he made retrospective accommodations for it in The Hobbit. These few but significant changes were integrated into the second edition. Further editions followed with minor emendations, including those reflecting Tolkien's changing concept of the world into which Bilbo stumbled.

I also discovered that Tolkien started writing the Silmarillion decades before the Hobbit, but originally intended it to be a book of English mythology. At what stage did it become the history of a fictional universe? How much of it had he written by the time he wrote the Hobbit?

How much of the history and mythology of Middle Earth was already in place in Tolkien's mind at the time of the Hobbit's writing and publication?

Answer 1

Christopher Tolkien's preface to History of Middle-earth 4 - the Shaping of Middle-earth provides the answer:

This book brings the 'History of Middle-earth' to some time in the 1930s: the cosmographical work Ambarkanta and the earliest Annals of Valinor and Annals of Beleriand, while later than the Quenta Noldorinwa - the 'Silmarillion' version that was written, as I believe, in 1930 - cannot themselves be more precisely dated.

This is the stage at which my father had arrived when The Hobbit was written. Comparison of the Quenta with the published Silmarillion will show that the essential character of the work was now fully in being; in the shape and fall of sentences, even of whole passages, the one is constantly echoed in the other; and yet the published Silmarillion is between three and four times as long.

So therefore the works that were in existence at the time that the Hobbit was written were:

• The Book of Lost Tales (this is the "Mythology for England")
• The Lay of the Children of Húrin
• The first version of the Lay of Leithian
• The Sketch of the Mythology
• The Quenta Noldorinwa (first major version of the Silmarillion)
• The Earliest Annals of Valinor and Beleriand
• The first Silmarillion map

Of course, the version of The Hobbit that Tolkien wrote in the early 1930s was not the very same as that which was published, and subsequent revisions occurred between then and it's publication date of 1937. During this time Tolkien also wrote:

• The first versions of the Fall of Númenor and the Last Alliance (including Mordor), bringing in the Second Age
• The Lost Road
• The Ambarkanta, "Of the Fashion of the World", (this was included in HoME 4 but Christopher Tolkien dates it to the later period)
• The Second Annals of Valinor and Beleriand
• The Ainulindalë
• Quenta Silmarillion (1937 version, that was submitted for publication as a potential sequel to the Hobbit, but rejected, leading to the writing of Lord of the Rings)
• The Lhammas, "Account of Tongues"

Elements in the Hobbit that were not new inventions but had already existed in these works include:

• The Necromancer (who was always intended to be Sauron) and Mirkwood
• The Three Kindreds of Elves
• Goblins (i.e Orcs) and Dwarves
• The High Elves journey to Valinor and the return of the Noldor
• "The Goblin Wars" (from context these are clearly the Nírnaeth Arnoediad)
• Gondolin
• Elrond and the "heroes of the North"
• Dragons and werewolves
• The Ruin of Doriath

The only major post-Hobbit additions to the legendarium were:

• The Rings of Power
• The Third Age
• The Events of the War of the Ring

Although of course all of the previously existing work was modified and (sometimes substantially) expanded, the basic structure and outline of the work remained quite fixed from the pre-Hobbit years.

As Christopher Tolkien says in his foreword to the Silmarillion:

In all that time The Silmarillion, considered simply as a large narrative structure, underwent relatively little radical change; it became long ago a fixed tradition, and background to later writings.

Answer 2

Tolkien didn't know anything about Gollum or how he got the ring. He also wrote a different view of trolls.

You have to understand that the Hobbit was more childish on purpose, and there were several retcons to connect it to Lord of the Rings.