The Silmarillion

After the downfall of Melkor at the end of the First Age, the Edain (Men who aided the Elves against Melkor) are given Númenor, an island of their own, away from the terrors of Middle-earth. It is located in the middle of the sea, between Middle-earth and Valinor. The Men there learn from the Elves and could “easily have surpassed the evil kings of Middle-earth in the making of war” (128) but choose peace instead. On Númenor, Men are forbidden to sail toward Valinor. Eventually, they begin to envy the Elves’ immortality, to the point where the Valar have to send a messenger to reason with them. For 2,500 years Númenor grows stronger; their ships sail far and wide, building colonies in Middle-earth where they are revered.

During this time, Sauron rises in power and becomes the second Dark Lord and makes Mordor his home. The Men of Númenor help the Elves (led by Gil-galad) who remain in Middle-earth as they fight against Sauron. As time passes, Men become more resentful and envious, as encouraged by Sauron. Eventually, they rebel against the Valar and the Elves. Their rebellion lasts almost 1,500 years. A line of kings continues this resentment until Tar-Palantir, the penultimate ruler, repents for his ancestors’ mistakes but it is too late.