The great conflict at the end of the Third Age, precipitated by the discovery that the Ring found by Bilbo Baggins in Gollum's cave is in fact the One Ring of Sauron. The war encompasses the Quest of the Ring-bearer (Frodo's journey to destroy the Ring in Mount Doom), the battles at Helm's Deep, the Pelennor Fields, and the Black Gate, and the machinations of Saruman in Isengard. It ends with the destruction of the Ring and the fall of Sauron, ushering in the Fourth Age of the world.