Afghanistan War (2001-2021)
After the 9-11 attacks, the United States learned that the al-Qaeda senior leadership, who took responsibility for the attacks, were based in Afghanistan. The ruling Taliban refused to surrender that leadership and shut down their facilities, and the U.S., also invoking the NATO treaty of collective defense, issued a conditional ultimatum that if the demands were not met, a new Afghanistan War would begin in 2001.
The U.S. already had clandestine paramilitary officers from the Central Intelligence Agency working in Afghanistan. United States Army Special Forces and other personnel under either the United States Central Command special operations component (SOCCENT), United States Special Operations Command, and other forces preceded the large-scale overt air attacks, designated Operation ENDURING FREEDOM, that started on October 7, 2001.