J.R.R. Tolkien's Middle-earth, the fictional world in which his novels "The Hobbit" and "The Lord of the Rings" take place, evolved over the course of his various works.
In "The Hobbit," Middle-earth is portrayed as a relatively peaceful and unchanging place, with the main conflict arising from the quest to reclaim the Lonely Mountain from the dragon Smaug.
In "The Lord of the Rings," however, Middle-earth is depicted as a world on the brink of destruction, with the rise of the Dark Lord Sauron and his armies threatening to enslave all free peoples. The story follows the quest of a small group of hobbits and their companions to destroy the One Ring, which is the source of Sauron's power.
In "The Silmarillion," a collection of stories and essays on the mythology and history of Middle-earth, Tolkien expands on the backstory of the world and its inhabitants, including the creation of the world and the rise and fall of powerful kingdoms and races. He also added more historical context to his world, such as the First Age and the War of the Jewels and the Second age, which is the age of Numenorean and the rise of Sauron.
Tolkien continued to work on Middle-earth throughout his life, and many of his notes, drafts, and other materials were published posthumously, including "The Children of Hurin," "The History of Middle-earth," and "The Unfinished Tales." These works provide further insight into the evolution of Middle-earth and its inhabitants.
In summary, Middle-earth evolved from a relatively peaceful and unchanging world in "The Hobbit" to a world on the brink of destruction in "The Lord of the Rings" and then became more detailed and complex with the addition of historical context and backstory in "The Silmarillion" and other posthumously published works.