War drives the plot points and shapes each of the characters in The River Between Us. In the frame story, the US is preparing to enter World War I, while the main story revolves around the Civil War. None of the transformations in the book would happen if not for imminent war. Though Howard doesn’t realize it, Grandma Tilly tells him the family’s story to prepare him for the realities of war. Within the story she tells, Delphine and Calinda would never have left New Orleans and stopped at Grand Tower if the Civil War had not been imminent. This action alters the course of their own lives and the lives of the Pruitt family members. War is the reason Noah leaves the house, provoking Mama’s crisis and prompting Tilly to leave Grand Tower for the first and last time.

Growing up during war shapes the characters’ identities. Tilly, Delphine, and Noah each assume the responsibilities of adulthood prematurely during the war. While they are in Cairo, Tilly and Delphine experience the harsh realities of war. Tilly writes, “We slept fast and deep through the brief nights, and hardly had the time to look up from our days, or to notice that we weren’t girls anymore” (91) Though Tilly and Delphine were only 16 and 15 years old, respectively, they fill the roles of women, nurses, and mothers for the sick soldiers, which forces the girls to grow and mature more quickly.