When Amir and Baba left Afghanistan, Amir was still a young boy. During the time he and his father spent in California, Amir grew into a mature, confident young man. He continued his love of writing and eventually graduated from college and got married. This transition from boy to man sat well with Baba, and he came to admire his son. The two of them lived together and bonded as they had never done in Kabul, sharing their weekends and working at the San Jose flea market. Although Amir never grew into the strong, physical man that Baba had been (and had hoped for in his son), the son made his father proud, and the two men grew closer than they had ever been. Amir's engagement and eventual marriage to Soraya gave Baba one last gift of happiness, presenting him with a daughter (-in-law) that Baba never had, as well as a closer relationship with General Taheri, who like Baba, had been a powerful man in his homeland before immigrating to America. Just as Baba had taken care of Amir when he was young, Amir tended to Baba in his final days, and Amir's love for his father was evident at the end--something that was not always present as a boy growing up in Kabul.
Amir becomes more Americanized, while Baba loses the power he enjoyed in Afghanistan. The characters both must adapt to the new culture so Baba relies more on Amir while still clinging to his Afghan culture. Eventually, the tensions between the two, which defined their relationship in Afghanistan, eases. Baba remains stubborn, but respect for his son grows.
The cold relationship between Amir and Baba seems to thaw a little with their arrival in America. This may be because of the lack of guilt that Baba feels after he not longer has the wealth and luxury that he cannot share with his hidden son, Hassan. This enables him to approach Amir in a more affectionate manner. The fact that Baba has lost all of his friend and is cut from his old social ties could also be the reason for the improvement in his relationship with Amir. This is because he is left with no other distractions, allowing him to focus more on his son. This cut from his friends presents Amir as his only true compannion to share his feelings with.