e did not actually defeat Sauron himself. The invasion fleet of the
Númenóreans was so powerful that Sauron's armies deserted him. Sauron
merely pretended to humble himself; to be carried back to Númenor as a
supposed hostage was exactly what he wanted. His plan was to weaken Númenor
as a war power by manoeuvering them into sending a fleet to attack Valinor,
where it would presumably be destroyed. He succeeded up to a point, but the result was disastrously more violent than he foresaw, and he was caught in the Fall of Númenor. Only his physical body perished since by nature he was of the spiritual order. Tolkien: "That Sauron was not himself destroyed in the anger of the One is not my fault: the problem of evil, and its apparent toleration, is a permanent one for all who concern themselves with our world. The indestructibility of spirits with free wills, even by the Creator of them, is also an inevitable feature, if one either believes in their existence, or feigns it in a story." [Letters, p. 280].