The non-profit National Security Archive at George Washington University is the place to go to understand the debacle of Afghanistan.
The Archive provides original sources. not opinion. In Afghanistan 20/20: The 20-Year War in 20 Documents, the Archive enables you to go beyond recycled punditry
The documents detail ongoing problems that bedeviled the American war in Afghanistan from the beginning: lack of “visibility into who the bad guys are;” Pakistan’s double game of taking U.S. aid while providing a sanctuary to the Taliban; “mission creep” as a counterterror effort against al-Qaeda morphed into a nation-building war against the Taliban; Washington’s attention deficit disorder as the Bush administration pivoted to invading and occupying Iraq; endemic corruption driven in large part by American billions and secret intelligence payments to warlords; fake statistics and gassy metrics not only by the military but also the State Department, US AID, and their many contractors; the mismatch between Afghan realities and American designs for a new centralized government and modernized army; and more.
To make a long story short:
Source: Afghanistan 20/20: The 20-Year War in 20 Documents | National Security Archive