Historical Fiction
World War II and its aftermath are central to the major plot points in this novel, shaping the book's central love stories (between Hatsue and Ishmael and Hatsue and Kabuo) and driving the fear and racism that contribute to Kabuo being put on trial. Although San Piedro itself is fictional, Japanese internment was quite real, as was the camp where Hatsue and Kabuo are imprisoned, Manzanar.
In addition, we get a gritty fictionalized account of the Battle of Tarawa (an actual event) through Ishmael's eyes. Beyond just giving us historical detail about the battle, Ishmael's account vividly portrays the gruesomeness of war and its impact by bringing our protagonist into contact with its horrors. The best historical fiction takes an accurate account of historical events and ups the ante by throwing in characters we care about, and that is certainly Guterson's idea here.