J.R.R. Tolkien > Akallabêth >
After the end of the First Age and the overthrow of Morgoth, the Valar created a land between Middle Earth and Valinor for the Edain, those men who fought on the side of the Noldor and the Lords of the West during the War of Wrath. The land was known to the Eldar as Andor, the Land of the Gift, for it was a gift from the Valar to the Three Kindreds of the Edain.
The Edain led by Elros were led to that new land in the West by the Star of Eärendil, so it was also known in after days as Elenna, or Starwards, and Westernesse, or Númenor (more fully Númenórë) in Quenya. They took Elros, the son of Eärendil, to be their first king, and the people of that land were collectively known as the Númenoreans, or the Dúnedain. They were the most blessed among Men, in that their span of years was longer than that of ordinary men (Elros himself lived 500 years, and the other people of his realm had on the average twice the average span of life for men in other parts of the world) and were not subject to disease, before they were seduced by evil. However, their numbers increased only slowly as a side effect of their lengthened span of life.
The land itself was shaped like a star, whose five branches were named Andustar, Forostar, Orrostar, Hyarustar, and Hyarnustar. The central heartland where the great capital of Armenelos was afterwards built, and where the holy mountain of Meneltarma stood was named Mittalmar, but their first city and old capital was Andúnië on the western shores of Andustar.
The Númenóreans were banned by the Valar from sailing so far west that the coasts of Númenor could no longer be seen, so that the Dúnedain would not be tempted to seek the Blessed Realm, and thus overstep the limits set upon them and on humankind in general by Ilúvatar. Of course, 25 generations after Elros Tar-Minyatur the Númenóreans did exactly that under the leadership of their last king Ar-Pharazôn the Golden. The Valar relinquished their power over the world for that time, and Ilúvatar sank Númenor beneath the sea, punishing the Númenóreans for their presumption and made the world round. See the Akallabêth node for more details.