Summaries of chapters in A Thousand Splendid Suns are included in the study guide for the novel--you can follow the link below to the chapter summaries.
Basically, in Chapter 49 of the novel, the story is moving towards its resolution. Laila and Tariq have gotten married in the previous chapter, and they are in the process of starting their lives together. The couple learns that the United States has declared war on Afghanistan, and Tariq thinks that war might not be such a bad thing if it gets Afghanistan's government in order. However, Laila does not agree because she knows that many people will die during the war. Also in this chapter, Tariq shows that he can be a good father to Zalmai who is upset because he misses his own father Rasheed.