What external conflicts exist with Amir and Hassan in The Kite Runner?
Between Amir and Hassan in Hosseini's novel The Kite Runner, in addition to their tenuous friendship and bond, there exist several external conflicts. One of the primary conflicts between them is the difference in their cultures and social statuses. The fact that Amir is a Pashtun and Hassan is a socially less-desirable Hazara dictates much of their treatment by others and their impressions of each other. Amir is much wealthier and receives better treatment by the people at large than Hassan does as Amir's servant.
Another conflict is introduced through the villainous character of Assef. During their childhoods, Amir and Hassan have to face Assef in a couple of scenarios. In one, Hassan is able to rescue Amir from Assef by threatening him with a slingshot, but Assef later finds Hassan and rapes him in an alleyway. Assef, of course, later reemerges in the story as the character who is holding Hassan's son as essentially his sex slave. The redemption of Hassan's son, Sohrab, by Amir at the end of the novel creates a point at which the conflicts between Amir and Hassan are finally laid to rest.
One of the first external conflicts is introduced in Chapter 5 as Amir and Hassan run into Asef and some of his bullies and Assef taunts them both, calling them homosexuals, etc. This external conflict is escalated in Chapter 7 as Hassan is caught while running the kite and Asef rapes him because he will not give up the kite.
Another example of an external conflict is the Soviet invasion of Afghanistan but this isn't really central to the plot as much as the previous conflict.
You also have the external conflict between Amir and Asef that does not end until Chapter 22 when Asef beats Amir to a pulp and only stops when Sohrab shoots him in the eye with his slingshot.