Only later , when Tolkien wrote The Lord of the Rings , did he integrate the story of both Hobbit and The Lord of the Rings into his Middle-earth world . Many of the thematic and stylistic differences arose because Tolkien wrote The Hobbit as a story for children , and The Lord of the Rings for the same audience , who had subsequently grown up since its publication . Some differences are in minor details ; for example , goblins are more often referred to as Orcs in The Lord of the Rings .