Downfall of Númenor

The Downfall of Númenor (called the Akallabêth, "the Downfallen") was the cataclysmic destruction of the island-kingdom of Númenor at the end of the Second Age, when its people, corrupted by Sauron and grown proud against the ban of the Valar, assailed the Undying Lands and were destroyed by the direct act of Eru Ilúvatar.

Númenor

Númenor was a great island in the western sea, granted by the Valar to the Edain, the Men who had aided the Elves against Morgoth in the First Age. There the Dúnedain grew tall, wise, and long-lived, building a mighty kingdom and becoming the greatest mariners of the world. But one ban was laid upon them: they might not sail west out of sight of their own shores toward the Undying Lands, which were forbidden to mortals.

The corruption

As the ages passed, the Númenóreans grew ever more powerful but also more fearful of death and resentful of the ban. In the days of the last king, Ar-Pharazôn, Númenor's might was so great that Sauron suffered himself to be taken captive and brought to the island. There, as a counsellor, he corrupted the king and most of the people, turning them to the worship of Morgoth and feeding their fear of death and their envy of the immortal Valar.

The assault and the Downfall

At Sauron's urging, Ar-Pharazôn raised a vast armada and sailed west to make war upon the Valar and seize immortality by force, breaking the ancient ban. When the fleet landed upon the shores of Aman, the Valar laid down their guardianship of the world and called upon Eru. Eru intervened directly: the great army of Ar-Pharazôn was buried, the island of Númenor was swallowed by the sea in a vast cataclysm, and the world was changed and made round, with the Undying Lands removed forever beyond the reach of mortal ships.

The survivors

A faithful remnant, who had not joined in the rebellion, escaped the Downfall in ships led by Elendil and his sons Isildur and Anárion. They came to Middle-earth and founded the realms in exile, Arnor and Gondor, carrying on the line and the heritage of Númenor. The Downfall ended the proud kingdom of the Sea-kings, but Sauron himself, though his body was destroyed, escaped to trouble the world again.