Readers of the bestselling novel, "The Killer Angels," or viewers of Ted Turner's movie "Gettysburg" and PBS's "The Civil War" have become familiar with Chamberlain and Alexander, two men who made their mark on history. This dual biography of the two officers-one Union and one Confederate-describes a number of Civil War battles, from Bull Run to Appomattox. The climax of each man's career, just as in the war itself, however, came at Gettysburg, where...