Answer:
the South's geographical advantage in the Civil War
Step-by-step explanation:
Although Janeczko´s non-fiction novel is aimed to explore the stories of real, and sometimes famous, spies in the history of The United States, this particular passage refers exclusively to the geographical advantage Southerners had during the Civil War.
Given that Southern states were the most often place for the confrontation, the Confederate spies found it easier to be safe, while the Union spies were at a disadvantage because they were in an unknown and unfriendly region.