Number One on the list:
For Whom the Bell Tolls by Ernest Hemingway
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Before I entered the U.S. Naval Academy as a young man, I'd read "For Whom the Bell Tolls," a book that helped bring home to me one of the fundamentals of military experience: what it is that moves soldiers in battle. Clashing ideologies and interests might be the genesis of war, but for the soldier any conflict comes down to fighting for his brothers. In Ernest Hemingway's novel, the main character, Robert Jordan, is an American teacher who has joined the International Brigades; he is an idealist battling against fascism in the Spanish Civil War. But he becomes disenchanted -- not necessarily with his cause but with its leaders and with their foreign allies. Still, in the end, Jordan voluntarily sacrifices his life for the sake of the people he fought alongside, the people he had come to love. Hemingway himself was not a veteran, but he saw war close up in the ambulance corps in World War I -- a perspective that gave him a profound grasp of the instinct that binds warriors together.