Andrew Coddington 
Code Breakers and Spies of the Civil War [PDF ebook] 

The United States in the 1860s seemed poised to become one of the world’s leading powers. Even with the benefits of new innovations such as the railroad and the telegraph, which brought the country together, unresolved issues between the North and the South broke the country in half. This book explores the ways in which the day’s new technologies changed the face of warfare and how, in this bloody war for unity, spies from all walks of life, including immigrants, women, and black people, contributed to the struggle.