From May 1996, Osama bin Laden had been living in Afghanistan along with other members of al-Qaeda, operating terrorist training camps in a loose alliance with the Taliban. Following the 1998 U.S. embassy bombings in Africa, the U.S. military launched submarine-based cruise missiles at these camps with limited effect on their overall operations.
The UN Security Council had issued Resolutions 1267 and 1333 in 1999 and 2000 directed towards the Taliban which applied financial and military hardware sanctions to encourage them to turn over bin Laden for trial in the deadly bombings of two U.S. embassies in Africa in August 1998, and close terrorist training camps and also children terrorist training camps.
September 11, 2001 attacks
Main articles: September 11 attacks and 9/11 Commission
Six days after the events of September 11, 2001, U.S. President George W. Bush identified Osama bin Laden as the 'prime suspect' in the attacks. Osama bin Laden was understood to be in Afghanistan at the time. On September 20, 2001, in an address to a joint session of Congress, President Bush issued an ultimatum demanding that the Taliban government of Afghanistan:
deliver al-Qaeda leaders located in Afghanistan to the United States authorities
release all imprisoned foreign nationals, including American citizens
protect foreign journalists, diplomats, and aid workers in Afghanistan
close terrorist training camps in Afghanistan and "hand over every terrorist and every person and their support structure to appropriate authorities"
give the United States full access to terrorist training camps to verify their closure
"They will hand over the terrorists or they will share in their fate" said Bush. No specifics were attached to the threat, though there followed a statement suggesting military action: "Our war on terror begins with al Qaeda, but it does not end there."
The Taliban government responded through their embassy in Pakistan, asserting that there was no evidence in their possession linking bin Laden to the September 11 attacks. They also stressed that bin Laden was a guest in their country. Pashtun and Taliban codes of behavior require that guests be granted hospitality and asylum.
On September 22, 2001, the United Arab Emirates, and on the following day, Saudi Arabia withdrew their recognition of the Taliban as the legal government of Afghanistan, leaving neighboring Pakistan as the only remaining country with diplomatic ties.
On October 7, 2001, before the onset of military hostilities, the Taliban did offer to try bin Laden in Afghanistan in an Islamic court. This offer was rejected by the U.S., and the bombing of targets within Afghanistan by U.S. and British forces commenced the same day.
October 14, 2001, seven days into the U.S./British bombing campaign, the Taliban offered to surrender Osama bin Laden to a third country for trial, if the bombing halted and they were shown evidence of his involvement in the September 11 terrorist attacks. This offer was also rejected by U.S. President Bush, who declared "There's no need to discuss innocence or guilt. We know he's guilty."
The United Nations Security Council (UNSC) did not authorize the U.S.-led military campaign in Afghanistan (Operation Enduring Freedom). There is some debate as to whether UNSC authorization was required, centered around the question of whether the invasion was an act of collective self-defense provided for under Article 51 of the UN Charter, or an act of aggression.
Also, the U.S. Administration did not officially declare war, and labeled Taliban troops and supporters terrorists rather than soldiers, denying them the protections of the Geneva Convention and due process of law. This position has been successfully challenged in the U.S. Supreme Court and questioned even by military lawyers responsible for prosecuting affected prisoners.
On December 20, 2001, the UNSC did authorize the creation of an International Security Assistance Force (ISAF) with authority to take all measures necessary to fulfill its mandate of assisting the Afghan Interim Authority in maintaining security. Command of the ISAF passed to NATO on August 11, 2003.