In chapter 20 we can see how people are oppressed because of the Taliban, because when Farid and Amir arrive to Kabul they meet some Taliban, Amir was going to tell them something, but Farid stops him, because they use anything to attack other people, especially when they go against them, that shows that they are oppressing people and their thoughts, so they are not free to express themselves.
Causes: Lack of control by the authorities in terms of punishing people, lack of police and government presence, lack of education and little control over the population.
Effects: people cannot express themselves and are not free to think, for fear of dying.