By J.D. Carruthers
The United States’ longest war began in Afghanistan on October 7, 2001 with the launching of Operation Enduring Freedom. The immediate cause for the war began with a series of events a month earlier. On September 9th, the commander of Afghanistan’s Northern Alliance Ahmed Shah Massoud was assassinated in a suicide bombing attack by agents of the terrorist organization al-Qaeda. The assassination set the stage two days later for 19 al-Qaeda agents led by Mohammad Atta to hijack four commercial airplanes loaded with passengers and deliberately crash them into the North and South towers of the World Trade Center in New York City; into the Pentagon in Arlington, Virginia; and into a farm field near Shanksville, Pennsylvania. One week later, President George Bush signed a joint resolution authorizing the use of military force against the terrorists who had attacked the US homeland. The mastermind of the September 11 attack was Osama bin Laden who was hiding in Afghanistan under the protection of the (fundamentalist?/extremist?) Taliban regime led by Mullah Mohammad Omar.
The initial phase of Operation Enduring Freedom proceeded at a rapid pace beginning with a bombing campaign by the U.S. Air Force targeting Taliban forces. By November 9, 2001 the Taliban regime was beginning to collapse after their defeat at Mazar-e-Sharif by Northern Alliance forces supported by U.S. Special Forces. A string of Northern Alliance victories at Taloquan, Bamiyan, Herat, Kabul, Jalalabad, and Kabul soon followed and completed the collapse of the Taliban by December 9. The Taliban leader Mullah Omar fled to Pakistan and Osama bin Laden reportedly took refuge in a mountain cavern hideout at Tora Bora. Afghan allies working with Special Forces surrounded the mountain hideout and systematically reduced the stronghold, inflicting heavy casualties on al-Qaeda forces. Bin Laden escaped apprehension during this operation, but was finally killed in during Operation Neptune Spear, a raid by SEAL Team 6 on a walled compound in Abbottabad Pakistan on May 2, 2011.
The second and longest phase of the Afghanistan War began after the collapse of the Taliban regime and the flight of Mullah Omar and Osama bin Laden to Pakistan. During the next 13 years, U.S conventional forces occupied Afghanistan and conducted combat operations against scattered Taliban forces while supporting efforts to stabilize Afghanistan’s political, economic and social institutions. The stabilization process proved to be a difficult challenge given that Afghanistan had been ravaged by war conditions bordering on anarchy for over 20 years. United States military involvement in Afghanistan came to a close when President Barack Obama announced that on December 28, 2014, Operation Enduring Freedom would officially end and the Afghan security mission would be fully transferred to the Afghani military.
During the course of the Afghanistan War, 2,356 U.S. service members were killed in action and 17, 674 were wounded.
 9/11 Commission Report executive summary
 9/11 Commission Report p. 65
 US Army in Afghanistan Operation Enduring Freedom p. 8