The International Security Assistance Force (ISAF) was a multinational military mission in Afghanistan from 2001 to 2014. It was established by United Nations Security Council Resolution 1386 pursuant to the Bonn Agreement, which outlined the establishment of a permanent Afghan government following the U.S. invasion in October 2001. ISAF's primary goal was to train the Afghan National Security Forces (ANSF) and assist Afghanistan in rebuilding key government institutions; it gradually took part in the broader war in Afghanistan against the Taliban insurgency.

The War in Afghanistan was an armed conflict from 2001 to 2021. It was the direct response to the September 11 attacks. It began when an international military coalition led by the United States launched an invasion of Afghanistan, declaring Operation Enduring Freedom as part of the earlier-declared war on terror; toppling the Taliban-ruled Islamic Emirate and establishing the Islamic Republic three years later. The Taliban and its allies were expelled from major population centers by the US-led forces, supporting the anti-Taliban Northern Alliance; however Bin Laden relocated to neighboring Pakistan. The conflict officially ended with the 2021 Taliban offensive, which overthrew the Islamic Republic, and re-established the Islamic Emirate. It was the longest war in the military history of the United States, surpassing the length of the Vietnam War (1955–1975) by approximately six months.