The History of the Lord of the Rings

The series has four titles: 1. The Return of the Shadow, 2. The Treason of Isengard, 3. The War of the Ring, and 4. The End of the Third Age. The first three of these are volumes 6, 7, and 8 of The History of Middle Earth and are covered there. "The End of the Third Age" is part one of Volume 9 in that series, Sauron Defeated.