When are people willing to sacrifice for the common good? What are the benefits of friendship? How do communities deal with betrayal? And what are the costs and benefits of being in a diverse community? Using the life histories of more than forty thousand Civil War soldiers, Dora Costa and Matthew Kahn answer these questions and uncover the vivid stories, social influences, and crucial networks that influenced soldiers' lives both during and after the war.

Drawing information from government documents, soldiers' journals, and one of the most extensive research projects about...