Hosseini discusses the ethnic tensions that exist even still in Afghanistan mainly through several of the novel's key relationships.
1. Amir and Hassan: Amir seems himself as better than Hassan not only because Hassan is a servant, but mainly because Hassan is a Hazara. Amir has been taught in school and through the other Pashtuns who surround him, that Hazaras are unimportant, unintelligent, and good only for manual labor. At first, Amir seems interested in finding out the truth about Hazaras (who are of Mongol decent) by reading one of his mother's books, but when he questions one of his teachers about the Hazaras, he scoffs at the notion that they have any history or worth. In part, Amir's view of Hazaras enables him to sacrific and betray Hassan for a kite. Because he does not view Hassan as being on the same human level as he is, Amir sees the trade of Hassan's innocence for Baba's approval as fair.
2. Hassan and Assef: Assef despises all Hazaras, and so his abuse and torture of Hassan and eventually Sohrab clearly demonstrates the view of many Talibs and other Afghan leaders toward the Hazaras. In reality, when the Talibs took over the country, they massacred the Hazaras. Because of the ethnic division which exists in Afghanistan, Hosseini is able to create a realistic villain in Assef.
3. Baba, Ali, and Sanuabar: When Baba's wife dies, he has an affair with his best friend's wife (Sanuabar). Admittedly, Hosseini describes Sanuabar as a beautiful woman, but it is because she and Ali are Hazaras that Baba feels entitled to commit such an act and hide it. He would have never treated another Pashtun in such a manner, because it would not have been socially acceptable. Thus, while Baba tries to atone for betraying his best friend, he would not have faced much social opposition if his relationship with Sanuabar had been discovered.