In a riveting narrative that puts diaries, letters and action reports to good use, British military historian Keegan (The Face of Battle, etc.) delivers a stunningly vivid history of the Great War. He is equally at easeAand equally generous and sympatheticAprobing the hearts and minds of lowly soldiers in the trenches or examining the thoughts and motivations of leaders (such as Joffre, Haig and Hindenburg) who directed the maelstrom. In the end, Keegan leaves us with a brilliant, panoramic portrait of an epic struggle that was at once noble and futile, world-shaking and pathetic. The war was unnecessary, Keegan writes, because the train of events that led to it could have been derailed at any time, "had prudence or common goodwill found a voice." And it was tragic, consigning 10 million to their graves, destroying "the benevolent and optimistic culture" of Europe and sowing the seeds of WWII. While Niall Ferguson's The Pity of War (Forecasts, Mar. 8) offers a revisionist, economic interpretation of the causes of WWI, Keegan stands impressively mute before the unanswerable question he poses: "Why did a prosperous continent, at the height of its success as a source and agent of global wealth and power and at one of the peaks of its intellectual and cultural achievement, choose to risk all it had won for itself and all it offered to the world in the lottery of a vicious and local internecine conflict?