Complex sentence: When Annatar was revealed as the Dark Lord Sauron, the Elves of Eregion tried to keep the Rings from falling in Sauron's hands, but only managed to rescue Vilya, Narya, and Nenya (the Three Rings of the Elves).
Split into simpler sentences: When Annatar was revealed as the Dark Lord Sauron, the Elves of Eregion tried to keep the Rings from falling in Sauron's hands. Sauron took most of the rings for himself, but the Elves managed to rescue Vilya, Narya, and Nenya, (the Three Rings of the Elves).