The War in Afghanistan was an armed conflict that took place from 2001 to 2021. Launched as a direct response to the September 11 attacks, the war began when an international military coalition led by the United States invaded 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 US-led forces supporting the anti-Taliban Northern Alliance; Osama bin Laden, meanwhile, 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.