The war in Afghanistan was a prolonged armed conflict lasting from 2001 to 2021. It began with the invasion by a United States–led coalition under the name Operation Enduring Freedom in response to the September 11 attacks carried out by al-Qaeda. The Taliban and its allies were quickly expelled from major population centers by US-led forces supporting the anti-Taliban Northern Alliance, thus toppling the Taliban-ruled Islamic Emirate. Three years later the US-sponsored Islamic Republic was established, but by then the Taliban had reorganized under their founder, Mullah Omar, and began a widespread insurgency against the new Afghan government and coalition forces. The conflict finally ended decades later 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 the September 11 attacks, masterminded by al-Qaeda leader Osama bin Laden, US president George W. Bush demanded that the Taliban immediately extradite him to the United States; the Taliban refused. After expelling the Taliban and their allies, the US-led coalition remained in Afghanistan, forming a security mission (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 under their founder, Mullah Omar, and began a widespread insurgency against the new Afghan government and coalition forces.