Stephen E. Ambrose, Band of Brothers (New York: Touchstone 1992). A noncritical but highly revealing study of the history of a single company from D-Day to the invasion of Germany.
Michael Bilton and Kevin Sim, Four Hours in My Lai (New York: Penguin, 1992). The definitive account of the U.S. massacre at My Lai and its aftermath.
Dee Brown, Bury My Heart At Wounded Knee (New York: Pocket Books, 1981). A history of the US genocide against native Americans.
Christopher R. Browning, Ordinary Men (New York: Harper Perennial 1992). The study of Reserve Police Battalion 101, a group of ordinary Germans asked to undertake the murder of Polish Jews. This is an interesting book to read in conjunction with Band of Brothers, above.
Paul Fussell, The Great War and Modern Memory (New York, Oxford University Press 1975). This is a fascinating, cynical treatment of the echo of the Great War in literature, theater and film. Fussell's Wartime (New York: Oxford University Press 1989) is a similar treatment of the second war.
Lt. Col. Dave Grossman, On Killing (Boston: Little, Brown 1995) analyzes the means by which we inure young soldiers to killing--and the social consequences.
Victor Davis Hanson, The Western Way of War (New York: Oxford University Press 1989). Hanson's mistitled book analyzes the Greek infantry battle for its lessons about the origins of modern warfare.
John Keegan, The Face of Battle (New York: The Viking Press 1975). Keegan, a former professor at the Royal Military Academy in England, analyzes military actions (and the personalities behind them) in clear and extremely original terms, debunking cliches and myths. This is his best book, examining three famous battles (Agincourt, Waterloo and the Somme). The kind of insight he gives: there is no such thing as "the shock of cavalry", as horses naturally do not run into each other.
Edward Luttwak, Strategy (Cambridge, Ma.: Harvard University Press 1987). A high level overview of military strategy, for the nuclear age. In The Grand Strategy of the Roman Empire (Baltimore: Johns Hopkins University Press 1976), he analyzes the decline of Rome from a strategic perspective.
Donald R. Morris, The Washing of the Spears (New York: Touchstone 1965). If you read only one book from this list, it should be this one. It is the most gripping work of history I have ever read. The story of the British destruction of the Zulu nation, it reveals the machinery of imperialism and genocide--while the story of the successful stand of 140 British soldiers against 4,000 Zulu troops at Rorke's Drift is one of the most dramatic war stories ever told.
Cornelius Ryan, The Longest Day (New York: Pocket Books 1969) and A Bridge Too Far (New York: Pocket Books, 1974). Both of these books, oral histories of the D-Day invasion and Operation Market Garden respectively, are excellent studies of the inevitable disruption of military tactics and the bravery of men fighting under chaotic circumstances.
Peter Singer, The Expanding Circle (New York: Farrar, Straus and Giroux 1981). Unfortunately out of print, this book charts the process by which we include an ever-widening group of people (and possibly other living things) in the inner circle of beings whose life is sacred.
Harry Holbert Turney-High, Primitive War (Columbia: University of South Carolina Press 1991). The classic study, originally published in 1949.
Michael Walzer, Just and Unjust Wars (New York: Basic Books 1977). A study of the morality of war.