In July 1883, just a few days after the twentieth anniversary of the Battle of Gettysburg, a group of editors at The Century Magazine engaged in a lively argument: Which Civil War battle was the bloodiest battle of them all? One claimed it was Chickamauga, another Cold Harbor. The argument inspired a brainstorm. Why not let the magazine's 125,000 readers in on the conversation by offering a series of articles written by officers in command of both...