Description:A word of explanation about how the information in this book was obtained, evaluated and used. This book is designed to present, as best my reporting could determine, what really happened.The core of this book comes from the written record—National Security Council meeting notes, personal notes, memos, chronologies, letters, PowerPoint slides, e-mails, reports, government cables, calendars, transcripts, diaries and maps.Information in the book was supplied by more than 100 people involved in the Afghanistan War and national security during the first 18 months of President Barack Obamas administration. Interviews were conducted on background, meaning the information could be used but the sources would not be identified by name. Many sources were interviewed five or more times. Most allowed me to record the interviews, which were then transcribed. For several sources, the combined interview transcripts run more than 300 pages. I have attempted to preserve the language of the main characters and sources as much as possible, using their words even when they are not directly quoted, reflecting the flavor of their speech and attitudes.