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.