Hosseini seems to have chosen women as his main characters in the novel to demonstrate how much they have suffered in his native Afghanistan under the Taliban regime. His first novel, The Kite Runner, is male driven and occurs mainly during a different time setting (the Golden Age of Afghanistan) and the time period right before 9/11 when the Talibs were most powerful.
Specifically, in A Thousand Splendid Suns, Hosseini portrays women being forced to ban together in order to survive. While Mariam and Laila most likely would not have been friends or helped each other under normal circumstances, under the oppression of their husband and the Taliban, they (like many real Afghani women) eventually recognize that they must work together to protect the innocent (themselves and the children).
This novel, like Hosseini's first, sheds light on the victims of totalitarian regimes, whether it be a certain ethnic group like the Hazaras in Kite Runner or women in this novel, Hosseini demonstrates that even in the most difficult setting, humans can persevere and eventually find their dignity. Mariam does so in this novel by sacrificing herself for Laila and the children and by being able to be at peace with herself, and Laila does so by continuing on and establishing a family with Tariq in spite of all that she endured.
I have just started reading this novel, but what I see so far is that the woman are there to be subservient to men. The story shows the courage of the woman and their friendships and issues as they deal with marriage, life's hardships, the disrespect of men, and the lack of education or the ability to progress out of the society that holds them.
It also shows how women cope and shows the inner strength of the woman in the novel. Mariam is a young girl married off to an abusive older husband who treats her badly and with contempt. Laila is then married to Mariam's husband to be his second wife. Her parents are killed and she is left in a difficult situation. She marries Rasheed because she is pregnant by her boyfriend and does not know what else to do.