How does this excerpt develop the central idea that espionage during the Civil War was often carried out by untrained citizens?

It shares the detail that the war kept going four years. The author builds up the focal thought that Elizabeth Van Lew was a spymaster amid the Civil War by including insights about the work that Van Lew did. The focal thought of the principal passage of The Dark Game is the Civil War endured longer than individuals at first anticipated that it would last.