War in Afghanistan (2001–2021)

The war in Afghanistan was a prolonged armed conflict lasting from 2001 to 2021. It began with an invasion by a United States–led coalition under the name Operation Enduring Freedom in response to the September 11 attacks (9/11) carried out by the Taliban-allied and Afghanistan-based al-Qaeda. The Taliban were expelled from major population centers by American-led forces supporting the anti-Taliban Northern Alliance, thus toppling the Taliban-ruled Islamic Emirate. In 2004, the U.S.-backed Islamic Republic was established, but by then, the Taliban, led by founder Mullah Omar, had reorganized and begun an insurgency against the Afghan government and coalition forces. The conflict ended as the 2021 Taliban offensive reestablished the Islamic Emirate. It was the longest war in United States military history, surpassing the Vietnam War by six months.

Following 9/11, masterminded by al-Qaeda leader Osama bin Laden, American president George W. Bush demanded that the Taliban immediately extradite him to the United States and close down al-Qaeda's camps in Afghanistan; the Taliban refused and demanded evidence of bin Laden's guilt before offering to hand him over to a neutral country. The US dismissed these offers and proceeded with the invasion. After expelling the Taliban and their allies, the American-led coalition remained in Afghanistan, forming the International Security Assistance Force (ISAF)—sanctioned by the United Nations—with the goal of creating a new democratic authority in the country that would prevent the Taliban from returning to power. A new Afghan Interim Administration was established, and international rebuilding efforts were launched. By 2003, the Taliban had reorganized and launched a widespread insurgency against the new Afghan government and coalition forces. Insurgents from the Taliban and other Islamist groups waged asymmetric warfare, fighting with guerrilla warfare in the countryside, suicide attacks against urban targets, and reprisals against perceived Afghan collaborators. By 2007, large parts of Afghanistan had been retaken by the Taliban. In response, the coalition sent a major influx of troops for counter-insurgency operations, with a "clear and hold" strategy for villages and towns; this influx peaked in 2011, when roughly 140,000 foreign troops were operating under ISAF command across Afghanistan.

An American covert operation in neighboring Pakistan led to the killing of Osama bin Laden in 2011, and NATO leaders began planning an exit strategy from Afghanistan. In 2014, NATO formally ended ISAF combat operations in Afghanistan and officially transferred full security responsibility to the Afghan government. Unable to eliminate the Taliban through military means, coalition forces (and separately, the Afghan government led by Ashraf Ghani) turned to diplomacy to end the conflict. These efforts culminated in the United States–Taliban deal in 2020, which stipulated the withdrawal of all US troops from Afghanistan by 2021. In exchange, the Taliban pledged to prevent any militant group from staging attacks from Afghan territory against the US and its allies. However, the Afghan government was not a party to the deal and rejected its terms. Coinciding with the withdrawal of troops, the Taliban launched a broad offensive throughout the summer of 2021, successfully reestablishing their control over Afghanistan, including the capital city of Kabul on 15 August. On the same day, Ghani fled the country; the Taliban declared victory and the war was formally brought to a close. By 30 August, the last American military aircraft departed from Afghanistan, ending the protracted American-led military presence in the country.

Overall, the war killed an estimated 176,000–212,000+ people, including 46,319 civilians. In addition, 66,650 people were killed in the related War in North-West Pakistan. While more than 5.7 million former refugees returned to Afghanistan after the 2001 invasion, by the fall of Kabul, 2.6 million Afghans remained refugees, while another 4 million were internally displaced.