Trauma
Trauma is a major theme in the novel. When Thomas returns to America he is profoundly damaged from his time in Vietnam. He continually has flashbacks to disturbing things he saw there, including the violent deaths of many soldiers and civilians. He is particularly haunted by the cruelty of the other American soldiers and the recurring image of his daughter running toward him as he is taken away in a helicopter. He also struggles with the fact that he killed the other people in his platoon when they were about to massacre a village of women and children. He feels he has done something wrong, because they were also American, but also doesn't know what he should have done instead. He is unable to speak about any of these experiences to anyone and becomes a recluse. Thomas's narrative indicates the way trauma has profoundly altered who he is and also left him trapped in his violent past.
War
War is one of the book's most significant themes. It is depicted in Thomas's narrative thread, showing the way his memories make it impossible for him to lead a normal life. At the same time, it also plays a major role in Lin's section of the book. Her life is torn apart by war. Her mother is killed by a landmine and her father is taken from her when American authorities come to Vietnam to reclaim him. Later, under the care of her grandmother, she is nearly killed in a conflict when a group of soldiers attacks her village. She spends the remainder of her childhood living on the streets of Ho Chi Minh City before being taken in by a couple that owns a flower shop. Lin's story, in some ways even more than Thomas's, shows how war wreaks havoc, robbing people of home, family, and stability.
Tradition
Tradition is another key theme in the book. Characters like Ruth and Thomas have reverence for the rituals of their ancestors and believe strongly in not straying from their beliefs. In contrast, characters like Dwight are happy to disregard these traditions if there is a chance to profit. This issue comes to the fore when a whale hunt is organized. Ruth believes it goes against tradition and is disrespectful to nature, and says so at a council meeting. Dwight ignores her and also plots revenge against her. Thomas participates in the hunt, but becomes disturbed by the way the other men disrespect the carcass of the whale. In this way, the book highlights how Dwight's rejection of tradition leads to discord in the tribe and harm to the natural world.
Family
Family is another important theme in the book. This theme is primarily explored in Ruth's storyline, as she struggles to care for her family in the face of terrible obstacles. When Thomas leaves for Vietnam, she is forced to raise their son, Marco, alone. Still, she does so diligently and lovingly. Later, after Marco dies and Thomas becomes a shut-in, she still brings tea and broth to Thomas's home. She shows a belief in the obligations of family, even when it puts significant strain on the person providing care. This obligation also appears in the older generations, like when Ruth's mother, Aurora, takes her in after she gives up the boat she was living on. These moments reveal how so often the burden of holding a family together falls on female characters like Ruth and her mother, Aurora.
History
History is another important theme in the book. Ruth and Thomas are constantly grappling with the loss of their culture. In particular, Ruth frequently thinks about how colonization has slowly ruined the lives of the people of her tribe, as they have lost much of their land, autonomy, and traditions. She grows increasingly concerned that the history of their tribe will eventually be erased entirely, as people forget rules and rituals. Ruth's worry reflects the decline of her tribe and the harm that has befallen her people. In this way, the book reveals how Ruth, and other characters like her, are hamstrung by their past, as their culture is under constant attack on multiple sides.
Nature
Nature is another key theme in the book. The elder members of Ruth and Thomas's tribe believe that nature is to be treated with respect, as it has a great deal of power and speaks to the people who are able to decipher it. At the beginning and end of the book, an octopus appears, signaling major moments in Thomas's life: his birth and reincarnation. People who view the octopus as sacred are forbidden from hunting it. Likewise, whale hunts are handled as a sacred activity in which the pursued whale is listened to by a chosen individual with the ability to stay underwater for long periods of time. Thomas is later disturbed when the men in the tribe participate in a whale hunt and disrespect the corpse of the whale. He is also later revived, mystically, by unseen natural forces. In the world of the novel, nature is a significant force that demands recognition.
Violence
Violence is also a major theme in the book. Thomas is continually disturbed by the cruel behavior of the men around him. He notes that Dwight has always been unkind to him and prone to violent retaliation against people who don't give him what he wants. Similarly, the soldiers in his platoon show no qualms about killing innocent people or desecrating corpses. This comes to a head when he decides to kill these other men in order to prevent them from massacring a village full of women and children. Thomas feels trapped, as he is forced to use violence to protect innocent people, but in doing so feels as though he has betrayed his country. Thomas begins to feel as though there is no escape from violence as he encounters it both at home and in the war.
