The protagonist of The Wars is Robert Ross, a young Canadian. The novel follows him from late childhood through his service in World War I to his death years later. Ross is a principled person who strives to meet the high standards he sets for himself. As a boy, he is devoted to his disabled sister, Rowena. After joining up, his experiences as a lieutenant in Europe dim his view of humanity as he and his close colleagues suffer at the hands of their own troops as well as the enemy. After he is seriously burned trying to save some horses, his injury forces him out of combat to recuperate in England.

Mr. and Mrs. Ross are Robert’s parents. Despite his good intentions, Tom Ross is weak-willed and ultimately undependable. His wife tries to cope with their daughter Rowena’s disability by self-medicating with alcohol. She opposes her son’s enlistment and questions the validity of the war itself.

Barbara d’Orsey is a beautiful British aristocrat who reacts to the war with a series of sexual liaisons with soldiers, including Robert. After his injury, she visits him in the hospital but makes sure he knows she has taken a new lover.

Juliet d’Orsey, Barbara’s younger sister, develops a crush on Robert while he is sleeping with Barbara. Later, after his injury, she becomes his caregiver/ companion.

Marian Turner is a hospital nurse in the combat zone who initially treats Robert after he is burned. She offers him the escape of overdosing on morphine, but he refuses.

Rodwell, a children’s book illustrator in civilian life, is one of Robert’s comrades. They serve together at the front and share a dugout. Rodwell’s gentle nature, shown by his love for animals, is crushed by the other soldiers’ cruelty, and he ends up dying by suicide. His death after the cat is burned foreshadows Robert’s injury after the horses die.