For starters, Ali and Hassan are members of a "lesser" religion, which does not allow for them to have any financial or social standing. In Afghanistan, if you are Hazara, you are destined to be lower class--no reading, no education, and doomed to a life of servitude.
Contrary to this, Baba and Amir lead a life of privilege due to their background. This makes life for Amir very easy and accounts for his very egocentric attitude, which lies at the crux of this novel.
Afghanistan was a place of turmoil, and people like Assef capitalized on the turbidity of the time and used their physical force, racist opinions and upper-class status to torment those deemed less worthy.
It is essential that the setting of this novel be in such a chaotic environment as one created by the political and religious unrest in Afghanistan. This turmoil allows people to take advantage of others and for the "haves" in society to reign over and further destroy the "have nots". All characters in this book are affected by this, and even when they move away from Afghanistan, they are still incredibly affected by their cultural history. Choices are still made based on the past because the culture and tradition, as well as the disorder and chaos, has become ingrained in the characters.