The reason for this division and for the different titles is that the narrative of the book does not follow a chronological order but moves backwards and forwards in time. Thus, it moves from the pre-war years to the war, back again to the pre-war period and finally again into the way years. This creates a sense of suspence for the characters' fate. In the Morning News interview linked below, the author explains she adopted this technique to keep the readers engaged and to feel free to experiment with form. She regarded these as fundamental points as she was writing a novel and not a political essay.