Middle-earth, or Endor in Quenya or Ennor in Sindarin, and in The Book of Lost Tales known as the Great Lands, is the name used for the habitable parts of Arda after the final ruin of Beleriand, and is east across the Belegaer from Aman. It is north of the Hither Lands, shown in the Ambarkanta, and west of the East Sea; and throughout the First and Second Ages it went through many colossal geographical changes, caused by Iluvatar.
Tolkien stated that the geography of Middle-earth was intended to align with that of our real Earth in several particulars. (Letters #294) Expanding upon this idea some suggest that if the map of Middle-earth is projected on our real Earth, and some of the most obvious climatological, botanical, and zoological similarities are aligned, the Hobbits' Shire might lie in the temperate climate of England, Gondor might lie in the Mediterranean Italy and Greece, Mordor in Sicily, South Gondor and Near Harad in the deserts of Northern Africa, Rhovanion in the forests of Germany and the steppes of Western and Southern Russia, and the Ice Bay of Forochel in the fjords of Norway. Far Harad may have corresponded with Southern Africa, and Rhûn corresponded with the whole of Asia. The Hobbit and The Lord of the Rings are presented as Tolkien's retelling of events depicted in the Red Book of Westmarch, which was written by Bilbo Baggins, Frodo Baggins, and other Hobbits, and corrected and annotated by one or more Gondorian scholars. Years after publication, Tolkien 'postulated' in a letter that the action of the books takes place roughly 6,000 years ago, though he was not certain.
Tolkien wrote extensively about the linguistics, mythology and history of the world, which provide back-story for these stories. Many of these writings were edited and published posthumously by his son Christopher.
Notable among them is The Silmarillion, which provides a creation story and description of the cosmology which includes Middle-earth. The Silmarillion is the primary source of information about Valinor, Númenor, and other lands. Also notable are Unfinished Tales and the multiple volumes of The History of Middle-earth, which includes many incomplete stories and essays as well as numerous drafts of Tolkien's Middle-earth mythology, from the earliest forms down through the last writings of his life.
The supreme deity is called Eru Ilúvatar. In the beginning, Ilúvatar created spirits named the Ainur and he taught them to make music. After the Ainur had become proficient in their skills, Ilúvatar commanded them to make a great music based on a theme of his own design. The most powerful Ainu, Melkor (later called Morgoth or "Dark Enemy" by the elves), Tolkien's equivalent of Satan, disrupted the theme, and in response Ilúvatar introduced new themes that enhanced the music beyond the comprehension of the Ainur. The movements of their song laid the seeds of much of the history of the as yet unmade universe and the people who were to dwell therein.
Then Ilúvatar stopped the music and he revealed its meaning to the Ainur through a Vision. Moved by the Vision, many of the Ainur felt a compelling urge to experience its events directly. Ilúvatar therefore created Eä, the universe itself, and some of the Ainur went down into the universe to share in its experience. But upon arriving in Eä, the Ainur found it was shapeless because they had entered at the beginning of Time. The Ainur undertook great labours in these unnamed "ages of the stars", in which they shaped the universe and filled it with many things far beyond the reach of Men. In time, however, the Ainur formed Arda, the abiding place of the Children of Ilúvatar, Elves and Men. The fifteen most powerful Ainur are called the Valar, of whom Melkor was the most powerful, but Manwë was the leader. The Valar settled in Arda to watch over it and help prepare it for the awakening of the Children.
Arda began as a single flat world, which the Valar gave light to through two immense lamps. Melkor destroyed the lamps and brought darkness to the world. The Valar retreated to the extreme western regions of Arda, where they created the Two Trees to give light to their new homeland. After many ages, the Valar imprisoned Melkor to punish and rehabilitate him, and to protect the awakening Children. But when Melkor was released he poisoned the Two Trees. The Valar took the last two living fruit of the Two Trees and used them to create the Moon and Sun, which remained a part of Arda but were separate from Ambar (the world).
Before the end of the Second Age, when the Men of Númenor rebelled against the Valar, Ilúvatar destroyed Númenor, separated Valinor from the rest of Arda, and formed new lands, making the world round. Only Endor remained of the original world, and Endor had now become Eurasia.
Elven languages which would later become known to us as Quenya, spoken by the Vanyar, Noldor, and some Teleri, and Sindarin, spoken by the Elves who stayed in Beleriand (see below). These languages were related, and a Common Eldarin form ancestral to them both is postulated.
Other languages of the world include
Adûnaic – spoken by the Númenóreans
Black Speech – devised by Sauron for his slaves to speak
Khuzdûl – spoken by the Dwarves
Rohirric – spoken by the Rohirrim – represented in the Lord of the Rings by Old English
Westron – the 'Common Speech' – represented by English
Valarin – the language of the Ainur.