Michael J. Wilson 
Afghanistan: The Afghan Papers, Troop Levels and Lessons Learned [PDF ebook] 

The United States has been in Afghanistan for almost 19 years. It is the longest war in the history of the United States. The mission of U.S. forces in Afghanistan has evolved considerably since 2001, when the United States initiated military action against Al Qaeda and the Taliban government that protected the group in the wake of the September 11, 2001 attacks. The United States needs to decide whether to continue America’s longest war and what the mission in Afghanistan is today.